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Self-heated vs DIY warming
difference in efficiency vs a diy setup with
It's not so much an efficiency issue as economics and charging opportunity issue.
The economics issue is straightforward; self-heated solutions tend to cost much more than DIY. For a while there the premium was +$200.per battery.
The charging opportunity issue is murkier. Imagine freezing overnights followed by a half-hour drive in the morning with a 30A DC-DC.
* a battery with warming pad that consumed 60Wh overnight to stay above freezing. * a self-heating battery that is below freezing
The externally warmed bank accepts current immediately and takes 15Ah of recharge. The self-heated battery shunts 60w to the heater (leaving 10A of charging unused) until the warmth equalizes up to the temp sensors. Let's say this takes 20 minutes. So now we have only 10mins of actual charging and the bank gets 5Ah of recharge.
If one was charging by alternator only and only driving to/from work while stealthing in freezing weather it's conceivable the self-heated batt would get *no charging at all* because it wouldn't ever get out of the heating phase.
### counterpoint
If one charged by solar this delay time is less important; the warming would happen throughout the day as needed. Even in the morning it wouldn't necessarily be a big deal because solar harvest might not be >60w anyhow.
### configurability
Also a control issue; with self-heaterts you don't get to pick your cell temp. After reading [this cell spec data](https://diysolarforum.com/threads/why-you-cannot-charge-lifepo4-below-0-degrees-celsius.2912/page-2#post-199774) I run my LiFePO4 quite warm, ~50F.
