Hi Kamil
, I have my batteries three years ago and they´ve run more than 2.000 miles in the C5 and in my electric tandem ( I use them in both vehicles). I use sealed betteries like this one:
http://www.ebay.co.uk/itm/12V-12AH-Battery-12-Volt-12-Ah-Battery-/250974914267?pt=UK_Computing_Networking_SM&hash=item3a6f4546db#ht_500wt_925I´ve two battery packets with three elements each one, so I have two batteries with 12 volts and 36 amp each. In a normal day, if I only must go to school with children and run into my city I only use one packet and I can run about 20 miles in the C5, more in my tandem. If I must go to my workshop, at the outside of the city, eleven miles away, I put both packets and I can get about 40 miles
.
After three years of use there are no signs of reduced autonomy or tired batteries (crossing my fingers meanwhile i write). This batteries has been the best choice I could to do. You can buy three at least and getting one more every time you need more autonomy and connect in paralel way and they need less room than a normal acid battery, almost the half and weight less also. I spent less than hundred pounds in the six 12 volts 12 Ah batteries, shipment costs included.
Regards, Rafael