I am experimenting with a buddy pack.
The idea is to constantly feed the IMA battery to make it use assist more and regen less.
I have a thread for it: https://www.insightcentral.net/forums...-pack-ze2.html
What I learnt is that hooking up an external power source to the IMA terminals generates an IMA fault code if there is any load or feed on the terminals at the moment you key on. So for starters, you need to be have the second pack switched off at the moment you turn the key or the car won't use assist at all.
Then there is a limit to how much amps you can put into the pack (about 17 Ampere); any more will trigger the IMA code.
A twin IMA pack can easily produce way more than that; and will when you enter EV mode, which makes the pack voltage drop by over 10 Volt.
So you need a good current restrictor (if you find one - I'm on the lookout for it so please let me in on your discovery
I'm using lamps now, but would prefer a device with a low voltage drop).
If you decide to work on an IMA battery bear in mind that several parts carry over 100 Volts; not just the big blue terminals, but also the smaller contacts with Phillips screws way down, and various other parts. These can kill.
So, you cannot practically double the IMA capacity without serious reconstruction in the batteries and BMS; it would be off limits but for the experts.
It would not have that much effect anyway; it would about half the voltage swings in the system, but that would just enhance it by a few %, and the whole hybrid part is just a few % of the total power usage. What remains is offset by the extra weight of the second pack.
The 0.6 kWh capacity makes it futile as a PHEV pack (my 1.4 kWh LiFePO4 buddy pack is much lighter and smaller, and even that has little impact).
So it is a good idea, but sadly not practically possible.
The one IMA battery in the car is doing a good job and is quite reliable too. That's why you can have a spare one cheaply
And +1 on what EricBecky said.
You cannot be too cautious.
Use fuses and relays, monitor what you do, test with the one hand rule, use rubber gloves, lock the kids and pets out...
Remember also that the 12V and high voltage systems are to be kept separated at all times.
So you cannot monitor the voltage with a cheap digital meter fed by the 12V system (trust me - I found out!). Those have some common ground and will trigger an IMA error. Use an isolated battery to feed any meters.
That is, if you do it. It ain't worth it.
I already know I will never earn back what I've invested in my project, nor would you if you try this.