So today I went to work on my flyer, for the first time in about 2 months, and used the 18ah battery I have borrowed. First thing was that it was a bit of a squeeze to get it in place on the bike. It does go in but no where near as smoothly as the original. The second thing I noticed was only four lights came on I thought I had fully charged it but seemingly not. With this in mind and given there was half an inch of snow on the ground the ride in wasn't much of a test. I had to switch to standard assist and the journey was slow but this is no fault of the battery. As soon as I got to work at 9:15 I put the battery on to charge. When I left sometime between 16:30 and 17:00 it had only just put all five lights to lit solid. My understanding is it is not fully charged till the lights go off. The journey home was far more impressive full power all the way and still two bars lit, this with new winter studded tyres fitted rather than the supplied marathon supremes. For me the real question is do I go for an 18ah or supplement my 10ah with either a 10 or 12 ah and swap mid journey.