Hi Mike, as daft as it sounds 20 Min's might be about right. You cant really gauge battery performance on time, only on miles driven & that depends on how heavy you are and how hilly your roads are. 20 Mins at 15MPH is about 6 miles. So that sounds about right (forget what the brochure claims)
I used a tom tom to tell me speed and distance before fitting a cycle computer to my good old C5.
The AH (amp hour) rating is a system that measures the amount of current the battery will deliver in one hour. The more the better - however the more usually means a bigger heavier battery, so its a trade off. The heavier the battery the more power will be needed, but remember the C5 can only draw 250 watts, so you get no performance advantage from a heavy battery; what you do get is more miles though !!
This is why I use the heavy Gel type batteries, I get a good 15miles before its half empty, and that's hilly power button full on and having to pedal 15 miles.
My son uses the new black Sinclair batteries and he only gets 7 miles per battery (takes two) and I’m a lot heavier than he is.
The original Sinclair battery was a 36AH deep discharge type, similar to what we now call a leisure battery - and was designed to be charged/discharged about 300 times, and give a steady rate of power. They were heavier than a car battery for the same physical size because they needed thicker lead plates.
A car battery its a little different, because a car battery is designed to give all its power in one go - so they are rated in staring amps and typically something like '470 AMP' that’s how much power it can deliver when you start your car - but remember the c5 will only draw about 20 amps while running (so no performance gain) & the problem with a car battery is that they way they are made the plates can bend with the constant charge/discharge cycles causing shorts and stuff (that’s why they aren’t supposed to last long), but the advantage is that they are much lighter than leisure batteries so for a short journey you might not need to pedal as much as your not carrying that dead weight.
So to sum it up - you can use car batteries they are lighter and may make the journey easier but the charge may not last as long (as in miles per charge) their life may be reduced.
Leisure batteries are the preferred type, but cost more and weigh more so you might need to pedal more (up hills or on the flat) , but they hold their charge better, and should last you longer. I must add though that a good car battery might be better than a cheapo leisure batteries.
Now on to the original question - sorry I got side tracked…..
The new black Sinclair batteries are not the same as the red type, I understand from Adam that they are 15% less than the red type. A friend went to work on one with me the other week, it’s a 6 mile journey 2x3 miles (hilly) and their and back took the battery to the last two lights on the pod. The battery also had an 8 hour stand between journeys - so it had chance to recover.
I have never had a working original - original, so I don’t have anything to compare it to, except to say I bought a Halfords type 038 and made a top I bought from c5Alive to fit it, and it performed the same, I had to cover it with gaffer tape and looks rubbish though, so I wanted one that says Sinclair on it - lol.