The Maplin Jump Start with 17Ah SLA which my wife bought me for Christmas (hints required - like price goes back up to £45 from £20 on the 24th) went back to the shop today. I wanted it for the cheap battery to provide power to an inverter running the boiler and central heating pump in the event of mains failure. It ran for precisely 10 minutes. No problem I'll just charge the battery. Nope, the 12v 500mA wart produced an unhealthy 3v (off load) and the charging LED remained black. So used the nice Lidl charger (Tronic T4X) which finished charging in 1.5 hours (now it charges at a max of 3.6A so that would be only about 5Ah into the "17Ah" battery). Anyway a simple car bulb load test showed 6A could be supplied for a full 15 minutes before the voltage dropped to below 10v (so about 1.5Ah). One final test using a power supply with voltage and current monitoring and charging to 14.8v produced similar results. Looking at some Chinese spec sheets a typical 17Ah battery (at the 20 hour rate) should supply 10 amps for an hour so this specimen was well duff. The shop said they sold 300 before Christmas and this was only the second returned (for a refund - stock was zero and would have to be ordered from head office).
Geo