[RedDevil]

EDIT: This is now a build thread! I bought 36 12Ah LiFePO4 cells, boxes, bridges, nuts, wires, connectors and BMS and am now done with tying these together.
Next phase: car harness...
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I want to design and build a portable battery pack and run it parallel to my Insight's hybrid battery.

The goal is to pull up the state of charge of the main hybrid battery so the IMA system will use the EV mode and boost more and to do away with forced recharge while running on gas.
It is not supposed to act as a full EV - both the Insights motor and the intended battery pack are not powerful enough for that.

The battery pack needs to be portable to charge it at home and at work at the mains with no fuss.
That should solve charging issues in cold or hot weather too.

It needs to have a (more or less) stable voltage corresponding to a high state of charge.

I don't want DC-DC converters in the parallel pack as I don't want the extra heat they provide, nor any overcharge issues.
A straight pack cannot overcharge the main hybrid battery when its fully charged voltage is below the max for the main battery.

Portable means I aim at no more than about 15 kilo / 30 pounds.
Charging voltage is 230 AC as customary in Europe.
Capacity needs to be at least 1 kWh; that should save me about half a liter of fuel per charge.

Total cost should not exceed 1000 € ($1100) by much, but I might stretch that for more capacity if worthwhile. Yet the aim is to have a ROI within the lifetime of the car for this mod.

I will break down the design over several posts and link them from here as a starting point.
Please do feel free to comment - I sure can use some help on this.

While we're at it a *** WARNING: Hybrid batteries contain high voltage components and can kill ! ALWAYS take the necessary safety precausions. *** so you know I know and I know you know, etc.

(I go bonkers for subtlety )

Some basics: power usage (2nd post)
The IMA hybrid system (3rd post)
Battery types

(thread under construction)