Battery Buffer (for Heater)

DIY
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1

Hi,

I have a heater in my boat (which is located 8m aft of my main battery). There is 12V cable connecting the main bank (via a fuse) with the heater. During the cold winter we realized, that the heater sometimes show below 12V (11,3 - 11,8 - 11,5V). Would like to fix this, by installing something light-weight, like a battery buffer. Making sure the heater gets constant voltage, without having to rerun all the cables, which is more than just complicated.

Do you have a good idea for something like this? I was thinking about a 50Ah 12V AGM (or LFP) Battery, which is then connected to the heater. The heater is a Autoterm 4D 4kW → which takes 56W of power according to the manual.

I’d like to build something lightweight, easy and cheap, but being able to operate the heater for around 4-6h.

Thanks already for your input.

2

Really no option but to replace the cable. Only other option would be to run a dc/dc converter at each end of the cable, and run the cable voltage at 24 or 48V.