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I would suggest that if you are not knowledgeable re electrical stuff, that you don’t build your own storage. Particularly now a days with the alternatives available.
Most people, even many electrical types, don’t realise the purpose of fuses, where to physically locate them and what type should be used as the first fuse (such as a HRC or other fuse that doesn’t maintain a spark under very heavy loads such as a short circuit)
Wire sizing, distribution etc can get confusing if you don’t allow for voltage drop at your max load.
12v batteries are not 12v. LiFePO4 are more around mid 13v (although about 14.6v charging max) down to around 11v. But from around 12.5 to 11 is a bit useless so thinking you have available the full power of a 12v battery is not a good idea. I have done lots of capacity testing of a couple of 100AH & 125AH batteries and they only meet their spec if you drain to around 11v.
Also, another bit of confusion if substituting LiPo for NMC batteries. LiPo is a construction method that could be NMC or LPF.
So if you measure your voltage drop from your battery, through switches, fuses, (hub devices with power switching) and ever decreasing cable sizes to the back of say your cooled camera, you will see a voltage drop under load (say cooler on full and imaging). I would allow about 0.5v drop on a good system but I’ve seen 1 or 1.5v drop.
So if you measure the capacity of a battery and stop at 12.5v (12v for gear and 0.5v drop), then you will have less power (maybe 10% but it depends).
If you have a very small setup, say an ASAIR, small camera and mount and a small dew heater, then probably 50 or 60AH is fine. Most people quickly add to that so I’d start with at least a 100AH. They are also more popular so you can probably get them cheaper.
Now a box such as Bluetti (I don’t have one but I’ve studied that particular box) usually use a 24v or 48v LiFePO4. This enables them to use a DC to DC converter to drop the full voltage discharge range down to around 13v. This gives you full access to the power in a battery. (This will be my next battery build method if I ever need to build more batteries for my rigs)
The complete units also usually have an indication of voltage/current/power being used and remaining capacity. They also already have built in fusing, charger etc. Something that a beginner doesn’t have to worry about.
While I’d still build my own because I can choose my gear (such as victron 30A charger and Victron Bluetooth shunt, Bussman fuse & powerpole connectors) and I don’t have to include the extra weight of a 240v inverter, I know what I’m doing.
If you are in ASNSW or NSAS, contact on chat and I can supply more info
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