IssacZachary wrote:Thanks! This would be awesome to do in connection with a LiFePO4 12V battery. Those die young do to the cold. Probably the reason they aren't used.
The other reason (aside from cost) is that lithium batteries require a BMS (unlike lead acid batteries, which just tie the cells together with what is essentially a bus) for long life, and the BMS not only adds more cost - it also adds the risk of failure and damage to or destruction of the cells.
Yes. Unbalancing can be problem with anything with lithium cells in series.
For the record, lead acid are not connected in parallel on a bus. They have the same series configuration that lithium batteries do. The difference is that they can tolerate being overcharged, whereas lithium cannot. So you can keep the cells balanced in a lead acid battery just by keeping it charged up to 100%.
Which brings up another problem with lithium. Lead acid batteries do best at 100% charge. Lithium batteries of any sort usually like being left charged at around 50%.
There are 12V lithium ion polymer batteries for sale designed for automotive purposes. I'm not sure how well the hold up or if they have balancing circuits. But what I do know is that they usually they don't have very low temperature ratings in their specs, except the ones made by Winston (formerly Thunder Sky).