The safe operating range for the different LiIon/LiPol cells is usually 4'C to 52'C.
Using or changing outside this zone is extremely unwise, as lipol are also exothermic during discharge.
Some sites regurgitate manufacturer specified limits as the range limits, but decent charge managers will fault if you try to exceed the SOA:
https://batteryuniversity.com/index.php ... mperatures
(you would never want to leave a Li cell cooking at 70+'C as they claim on some pages)
In general for Li cells:
below SOA temperatures cause capacity degradation, reduces discharge current limit, and charging can cause catastrophic failure.
above SOA temperatures cause capacity degradation, increase discharge current limit, and charging can cause catastrophic failure.
SLA glass pack pb batteries are #1 for standby systems, as these can:
1. Be constantly trickle changed (for a 12v pack at 25'C, that would be 13.4v at 10% Ah rating to prevent H2 gas venting.)
2. Will survive very low temperatures if fully charged (your electronics will fail before the battery)
3. There are temperature adjusted smart chargers for pb packs (and gel cells). In general some brands can do 64'C with some capacity loss, but their current output limit actually increases.
4. the cells can take abuse (think about the loads required to start a car), and most don't require smart chargers or fuel-chips to manage the pack
5. they usually fail "open" as they tend to boil off electrolyte (or swell if a gel cell), and can simply be checked with a volt meter
6. they are cheap for their capacity, and can be cycled for years if you never discharge below 11.2v on a 12v pack.
If your project doesn't care about weight, power density, or vertical mounting restrictions....
than SLA packs are the best value for capacity (gel cells are #2 as they only last a few years).
I would recommend splitting your project into two metal enclosures, and still use a SLA setup.
(we have some tested packs from 2006 still in operation today in 2018.)
Best of luck,