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What The Battery Cost Calculator Works Out
- Disposables per year: batteries in rotation x full changes a year x the price per alkaline. Eight cells changed six times a year is 48 batteries, GBP 24 at mid-range prices, every year, forever.
- Rechargeable setup: the one-off cost of a set of low-self-discharge NiMH cells and a decent charger, GBP 35 for eight cells at GBP 2.50 and a GBP 15 charger. Charger quality matters more than cell branding: independent-channel smart chargers that stop per cell beat the timer-based ones that quietly murder good cells.
- Verdict: the setup cost divided by the yearly disposable spend gives the payback in months, usually well under two years, followed by a decade of near-free power.
- Cells to buy, cell price and charger price (advanced): size the kit to your own rotation (a charged spare set standing by makes swap-and-charge as convenient as the bin) and price it from the shop you use. Good AA NiMH cells cost GBP 2 to GBP 4 each.
- Rated charge cycles (advanced): standard NiMH cells manage 500 or so cycles, premium Eneloop-style cells claim up to 2,100. The lifespan card divides the cycles by your changes a year.
- Electricity to recharge (advanced): each AA recharge draws about 3.5Wh from the mains including charger losses, so a year's recharging costs pennies at your unit rate, which defaults to the current Ofgem price cap.
- Cost per battery use (advanced): the rechargeable cell's price spread over its cycles plus the electricity per charge, against one alkaline. It is typically under a penny against 50p.
- Saving over the comparison period (advanced): the disposable spend over the years you choose minus the charger, every set of cells bought in that time and the electricity. Keep the exceptions in mind: smoke and CO alarms take exactly what the maker specifies, decade-sipping remotes and clocks spend alkalines so slowly that self-discharge wins, and a few devices sulk at NiMH's 1.2V.
- Housekeeping: buy cells in one batch and keep them in labelled sets so ages match, since mixed old-and-new is the classic capacity killer. Dead cells go in the supermarket collection tubs, never the household bin.