Here's a few random thoughts on Insight 12V system needs/batteries. I've been paying close attention to the 12V system for the last year or so, since I've been experimenting with a 12V battery made from Insight IMA sticks...
-In general, I've read that a lot of the 12V lead acid batteries for cars come from only a few or couple main manufacturers.
-I read that it's usually best to buy 12V lead acid from stores where turn over is high, so you don't get stuck with a battery that's been sitting on the shelf for too long.
-Some years ago I read that Wal-Mart 'Everstart Maxx' or something like that were good. Back then they had something like a 3 year free replacement, 5 year pro-rated warranty. I think it's less now. I had one in my van, that I let sit for long stretches, and it failed in a couple years...
-The stock 12V system, with IMA pack in place, everything working normally, dishes out pretty light duty on the 12V battery. It usually charges to about 13.8 to 14V, a bit higher when the engine is cold.
-The DC-DC converter goes into 'low power mode' sometimes quite often, such as during assist, when 12V system load is small (i.e. headlights and AC off, etc.), during auto-stop. At these times 12V system power comes from the 12V battery until voltage drops to about 12.1V...
-In 'low power mode' the car allows discharging down to about 12.1V, at which point the IMA pack begins to supplement the 12V system needs (i.e. energy is taken from the IMA pack to hold 12V system voltage at about 12.1V). So usually, the 12V battery operates between about 12.1 and 14V...
-We know that starting the car usually relies on the IMA motor/pack. The auxiliary starter motor draws about 1000W. It's been reported that current draw on a 12V lead acid was about 130 amps using the starter motor, that's about what I've seen as well, with voltage at about 7.8V but on a NiMH battery.
-If your IMA system is disabled/bypassed, the demands on the 12V battery are... pretty huge. 1) you rely on the 12V starter motor, which of course relies on the 12V battery, 2) the DC-DC converter doesn't put out any power at idle, so you're relying totally on the 12V battery at idle, 3) the IMA pack isn't there to supplement power when 12V system voltage drops below that 12.1V threshold any longer...
-12V system load is typically a minimum of about 140W (10 amps at 14V) while driving, and more like 224 to 280W like with climate control on and always-ON driving lights (Canadian models). With my IMA pack bypassed, I see about a 10-20 amp draw on my NiMH 12V battery at idle, when the DC-DC isn't putting out power cuz the engine speed is too slow... I'd have about 10 to 15 minutes sitting at idle with my NiMH battery before the battery drained...
-I've been using some really old, ~200,000 mile Insight sticks, 10 of the cells, for 12V battery for a few weeks now - with the IMA pack bypassed. Their total capacity is about 5.8Ah at 6 amps. Internal resistance is something like 3.5-4 mΩ per cell... They're pretty balanced, but pretty bad... yet they're handling the toughest-duty job possible, so far...