hello dai
the ones i use are only 17 to 20 ah
i used to get about 14 or so hours of use out of one before the lamp on the vari started showing low voltage
now i recharge every night regardless of whether i did 7hrs or 1hr
this has been working well so far
a proper purpose made charger would make em last even longer (so i have been told)
but they are around 50 quid
and as i speak i have one good battery on the van and two more equally good in the shed
what do you use to check the voltage on the battery
is it a voltmeter or am i being thick
