what i would do is some simple maths
charge the battery
up to max and give it a few extra hours just to be sur e
somewhere on the battey it wil tell you how many amp/hours it has fully charged
get a headlight bulb with know wattage and hook it up to battery
and time how long it takes to go flat
eg a 50 watt lamp running on 12 volts of about 4 amps ( W/V = Amps)
so divide the amps of the bulb into the amphours of the battery
eg a 6 amphour battery
should drive a 4 amp bulb 1.5 hours as i said not exact but its a pretty good test
this is a bit of a guess method because when the voltage drops it wont be the same amps
but if it goes flat in 5 minutes it will tell you
as for damage to all the EI stuff that is beyond my pay grade
discharge is not that simple .
a faster discharge ... results in less return.
it you try are draw 4 amps out of a 12 amp battery
it will release
about 9 amps in 2.75 hours and be dead .
... 3 amps are lost to heat in the battery
, the heat lost is caused by the speed of the chemical reaction .battery
companies use slower discharge rates to boost the label rating .
( the label rating is real , but only if slowly discharged over 20 hours )
image is for a typical 12 amp battery
... 0.6 amps x 20hrs = 12amps
The amp rating on the side of the battery
is based on a 20-hour discharge .
label amps / 20
i would use a 2 amp draw to test a motorcycle battery
... drawn down to 12 volts
... 2 amps is the brake light filament side of a dual filament bulb , typically about 27 Watts .
2 amps is about what the Boyer
/Pazon analog ignition uses .
So using a 2 Amp draw to 12 volts will tell you about 1/2 as long the battery
will feed the ignition
... you can drop down to 10 volts to get an exact time ... been a full drawdown test is harder on the battery
In either case the battery
should be recharged immediately .
a britbike doesn't need that much of a battery
... it's more of a limp home feature should the
Alternator/V.regulator fail .
its kind of nice to know just how far your bike will run on the battery
and not guess .
or carry a cell phone.