Lead acid battery cutoff voltage circuit

Question

I've developed a device that runs on a 12V lead acid battery. The device will be deployed at a location where we cannot have physical contact with it. It is therefor not possible for us to detect the battery's voltage.

I want the battery to last as long as possible, but I don't want it to deep discharge. For this reason I wanted to implement a low current voltage cutoff circuit, but I am having trouble finding any. There are several that 50-100 mA, which already is too much.

What are low current cutoff devices or how can I make one?

Answer 1

There are voltage monitor ICs, which perform this (or similar) functions, intended to disable (by logic signal) a circuit when voltage is low. This one LT2965 seems suitable for your needs. It works by detecting low voltage, and requires that your device take a logic signal input and cease consuming power. There is a small current drain (at 12V, something under 10 uA), but most batteries can handle that for a year or two.

A 'turn-off' threshold should be set according to the lowest charge state at the (coldest, if I understand lead-acid batteries) temperature. The 'turn-on' threshold should be slightly higher, so that diurnal temperature variations don't cause it to toggle.