Will switching to a larger 12V battery gain MPG?

[firsthonda]

If so, why do you think Honda went with such a small battery for the Insight II?

[jonniedee]

No - the 12v battery has nothing to do with propelling the car

[firsthonda]

I know it doesn't directly but some folks on this board go with a larger Civic battery in an effort to down on force regens. I'm not convinced it helps, that's why I stared this thread for discussion.

[joecvt]

Originally Posted by firsthonda

I know it doesn't directly but some folks on this board go with a larger Civic battery in an effort to down on force regens. I'm not convinced it helps, that's why I stared this thread for discussion.

The 12v battery is probably even a bit oversized from Honda....It only has to power up normal 12v items and the ECM / IMA electronics then the IMA system can supply the power. Even during AutoStop, under heavy electrical load, the DC-DC converter can still supply power to the 12v system. The most demand there would ever be on the 12v battery are those very rare occasions (typically cold climate) when the typical starter motor has to crank the engine instead of the IMA battery due to being too cold outside.

People that have added additional items to their car like amplifiers and all of that type of stuff probably should consider something larger than normal though.

An aged battery that needs more changing than normal should be changed out because the additional (above average) required charging reduces your overall MPG since the additional engergy has to come from somewhere (gas).

JoeCVT = Just your average CVT owner

[Cobb]

Huh???? The 12 volt battery powers everything but the IMA motor and engine. Gasoline powers the engine, the IMA battery powers the IMA motor and recharges the 12 volt battery. Everything else is powered by 12 volts.

That 12 volts has to come from somewhere. Either its recharged when regeneration takes place or when the "alternator" turns on and uses the IMA charge to charge it.

My conclusion is the oem battery cant store much, so its being fed by the IMA battery frequently. This in turns robs assist and causes more regens and less assist. The larger 12 volt battery allows more pause between the system recharging and powering the stuff in the car since it has a larger capacity.

I have a 2nd group 51 battery I hope to install this weekend. Currently in this below freezing VA weather with the new battery I am netting between 53-60 mpg. Cant wait to see any different. I will go the whole week. Then week after adding the subs and the BOOM, BOOM, BOOM back to my hybrid.

[joecvt]

Originally Posted by Cobb

Huh???? The 12 volt battery powers everything but the IMA motor and engine.

The 12v battery has to initially power normal 12v items in your car and supply initial power to your ECM / IMA computers until the contact relay kicks in and allows the DC-DC converter to get power from the IMA system and supply 12v power to your battery and the all of the other 12v items in your car....Once the IMA systems power up, the 12v battery acts more or less like a buffer for 12v but the power comes from the IMA system to do so. I tried to say that earlier in a much shorter description.

Originally Posted by Cobb

Gasoline powers the engine, the IMA battery powers the IMA motor and recharges the 12 volt battery. Everything else is powered by 12 volts.

If the 12v battery requires a charge, the DC-DC converter will handle that but it also handles ALL of the other 12v needs while it is active. There is an ELD device that will sense high 12v demand (like turning on the headlights for example) and any high 12v demand will keep the DC-DC converter active even if the 12v battery is charged.

Originally Posted by Cobb

That 12 volts has to come from somewhere. Either its recharged when regeneration takes place or when the "alternator" turns on and uses the IMA charge to charge it.

Yes...It does come from somewhere....AS I mentioned earlier, it comes from the DC-DC converter (you call it an alternator). However, your either / or scenario above is incorrect. When regen occurs, it supplies power to the IMA batteries (not to the 12v system directly). The DC-DC converter (what you say is the alternator) takes power from the IMA battery and converts it to 12v when needed. That is why it is called a DC-DC converter because it take high DC voltage from the IMA battery and converts it to a lower DC voltage (12v).

Originally Posted by Cobb

My conclusion is the oem battery cant store much, so its being fed by the IMA battery frequently. This in turns robs assist and causes more regens and less assist. The larger 12 volt battery allows more pause between the system recharging and powering the stuff in the car since it has a larger capacity.

A properly working OEM 12v battery can store enough to crank the engine using the typical starter motor that most people will never (or hardly ever) hear working when starting the engine. Honda had to install a battery that would handle the cranking amps required in that situation but most of the time, even the OEM size that Honda HAD to choose is not really needed.

By you putting in a larger battery that may have more capacity, you increase the "12v buffer size" but you do not affect the amount of work the DC-DC converter must do....Here is why:

Even if you did succeede in decreasing how often the DC-DC converter has to charge the battery, you must then increase the length in time it takes to charge the 12v battery during each cycle. Since all 12v charging power comes from the DC-DC converter, there is nothing saved by using a larger 12v battery since both small and large batteries still have to be recharged during whatever period of time you are driving.

JoeCVT = Just your average CVT owner

[cheesie]

yeah i dnt know much bout cars and i havent added anything that will need a bigger battery ( sound system ) but i did replaced the 12v battery with a group 51( like cobb) and for some reason ive got less to no regn when driving and my mpg went from 39.2 ( and was going down ) to 45mpg!!!
i also feel the car assts more


just yesterday i took a 40 mile drive and was checking the mpg screen, i couldnt believe it! my mpg was going up and up and up
first 42, then 45 and wen i got to my destination i scored a 49.2 mpg!!
i drove the same way i always do and stil the car gave me more mpg!!

i was really exited and was bout to make a post saying to everybody how to score more mpg's and to stop trading there insight for a prius ( seen that before )

however when i started driving again i saw my mpg was going down
weird

right now im on the avrg 45 ( still more than before : 39.2 )
idk y i went down, maybe cuz i was driving the streets during traffic, but i still drove the freeway later on with no traffic and i did ok


im still happy with my new battery: it gave my car more power
i just hope i stay over 45 mpg !

[Cobb]

Joe, you are not describing the charging/12 volt system correctly for the i2.

Maybe they changed the design since the first gen? I see by a scanguage that the dc-dc converter isnt always working or charging. In many cases its off and the car is running on 12.x volts. I only see it charge when first fired up for a few minutes, when regening and briefly when the voltage falls below 12.5 volts. Before I replaced my battery it was running constantly for the first few hours of my trips.

My geo metro on the other hand is running off the alternator once the engine is running. I see anywhere from 13.4-14.6 volts. When the engine is off its less than 13 volts by scanguage.

Having said that, a larger 12 volt battery allows a larger buffer between charges by the dc-dc converter. This is why cheeise is getting a drop in mpg. His battery was fully charged and the dc-dc converter wasnt needed or even working for a while til the voltage dropped. Now he is drawing down the charge and its putting it back using the power from the IMA battery. If cheeise starts to coast mores, engine brakes he can get back of exceed his previous mpg gains. I am netting 60mpg in below freezing weather.

Looks like we really need a better battery than lead acid since it will only take a surface charge and needs a long continues low charge.

I always put the largest battery I can in all my vehicles when I have to get a jump to start it. I precharge the battery too. I always use aftermarket lights and sometimes need to idle for an extended amount of time.

[joecvt]

Originally Posted by Cobb

Joe, you are not describing the charging/12 volt system correctly for the i2.

Maybe they changed the design since the first gen? I see by a scanguage that the dc-dc converter isnt always working or charging. In many cases its off and the car is running on 12.x volts. I only see it charge when first fired up for a few minutes, when regening and briefly when the voltage falls below 12.5 volts. Before I replaced my battery it was running constantly for the first few hours of my trips.

Perhaps they did change some part of the design but what you just described matches what I believe I am saying. I have never said that the DC-DC converter is always active....Here is a portion of my last post:

If the 12v battery requires a charge, the DC-DC converter will handle that but it also handles ALL of the other 12v needs while it is active. There is an ELD device that will sense high 12v demand (like turning on the headlights for example) and any high 12v demand will keep the DC-DC converter active even if the 12v battery is charged.

This also means that when the 12v battery does not need to be charged AND there is a low electrical load, the DC-DC converter is inactive. At that point, all 12v power is coming from the 12v battery UNTIL it needs re-charging OR the ELD senses a higher electrical load.

ELD units are not a new thing but just to make sure a 2010 Insight has an ELD unit, I check Majestic Honda:

Honda Automotive Parts

(item number 11)

This "tells" the ECM control unit how much electrical load is in use and IS part of a decision maker if the DC-DC converter becomes active or not.

It is not a big issue if you disagree about the DC-DC converter operations but you surely have to admit that the 12v charge comes from the IMA system no matter if it is a large capacity 12v battery or a smaller 12v battery capacity.

Both batteries eventually must be charged by the IMA system. I assume that you would also agree that the larger capacity battery will take LONGER to charge compared to a smaller capacity battery (assuming both batteries are in good condition and the same age). Perhaps the larger battery does not have to be charged as often but it will certainly take longer to charge during each cycle......

I guess time will tell but it is hard to come to any conclusion with a newly installed battery in comparison to an older smaller battery that also had to deal with additional audio electronics (or a dual battery setup).

I seem to recall your earlier postings that you were getting very high MPG when your car was newer so what has changed?

JoeCVT = Just your average CVT owner

[Cobb]

Your first para of your previous post just reads that the 12 volt battery is used to activate the relays, then its all ima.

I had a group 27 deep cycle battery in the rear of my car for the sub woofers. I noticed almost a year later it had been boiling over and acid had been spilling out in the ima compartment. I had someone tell me the larger battery superceeded the smaller one and it was a non issue unless the big battery had a problem.

I switched it out to a u1 agm I had. Now I have nothing in the back, next week hope to have the second group 51 there.

Originally Posted by joecvt

The 12v battery has to initially power normal 12v items in your car and supply initial power to your ECM / IMA computers until the contact relay kicks in and allows the DC-DC converter to get power from the IMA system and supply 12v power to your battery and the all of the other 12v items in your car....Once the IMA systems power up, the 12v battery acts more or less like a buffer for 12v but the power comes from the IMA system to do so. I tried to say that earlier in a much shorter description.