Thank you Roger, trouble with primary batteries is once they've done their job they need to be replaced. so not really economical on a system that may place a demand on them more than once within their shelf life.

The zinc- air batteries are often called ‘air alkaline’ in the literature

(more on that electric fence style model )

Cell voltage about 1.3,  a “9V” block is abit short really usually  6 cells.

shelf life unopened 2-3 years, reduces fast to some weeks once air is admitted. The KOH tends to draw in extra moisture so it is self diluting over time. In humid places a month or two once the air port is open.

Mike

Lead-acid car batteries must stay >70% charged to reach their rated number of charge/discharge cycles.  For Lead-acid Leisure, or ‘deep cycle’, batteries it's >50%. Ball park; self-discharge is around 3% per month, so if we assume your load takes 3% capacity per month out of the battery, we are losing 6% per month so hit the 30% limit in 5 months for a car battery and the 50% limit in 8 months for a leisure battery.

This is a bit off-topic but my first Job was in the lab at Vidor Batteries. We had Leclanche cells in the lab 20 years old which were taken out and tested periodically. It always amazed me that they were still capable of carrying load after all that time.

Vidor still had a line producing 250V dry batteries for portable radios at that time. I could never understand how the girls building the batteries didn't get electrocuted.

Vidor also made big batteries for rural GPO telephone sites where there was no mains electricity. The batteries were quite low voltage possibly 6 or 12V.

Another line was the SARBE battery which aircrew carried for their emergency transmitters.

Vidor had a ‘button cell’ pilot plant but quit development as they had the habit of exploding when being charged. The lab ceiling looked like it had been machine gunned !. Eventually, to prevent injury the chargers were fitted with plywood covers and fixed down during charging. If they had stuck at it Vidor might be around today.

Just before I left they were starting lead acid production. Not the healthiest place to work as I recall.

Good days when we actually had a lunch hour instead of sitting in front of a screen sending email whilst eating a bag of crisps.

CJ