My wheelchair originally uses lead acid batteries. Its range is only about 18km for 2 new 12V/35Ah batteries. Another problem of lead acid batteries is that their Ah capacity decreases quickly by time, then that makes the range decrease quickly too. In my case, the range is down to 10-15km just after 6 months.
I intended to move to lithium batteries and then I found our forums. I got much knowledge in lithium here. I knew there are 3 types of lithium (ion, lipo and lifepo4) and the lifepo4 is best for wheelchair batteries.
I also posted a thread to ask advices about upgrading to lifepo4.
viewtopic.php?f=2&t=5116
Burgerman commented that the lifepo4 battery pack I would purchase has a too small capacity (40Ah) due to my wheelchair's battery box's size. So the battery pack may not have enough concurrent discharging the wheelchair needs. And the capacity of 40Ah may not improve the range much. That made me a bit hesitant.
But I am too disappointed about my wheelchair's range. I always need a pair of lead acid batteries for spare. When I go somewhere a little bit far, my dad must bring the spare batteries to my location for replacing. So, I decided to make a risk with lifepo4.
I bought lifepo4 battery pack at pingbattery.com. Ping helped me to customize the batteries' size to fit into my battery box with max Ah capacity. So the last result was a pack of 24V/50Ah.
The battery pack is separated into 4 units, each unit is a battery of 6V/50Ah with 2 cables for connecting. They look built quality with solid cables and tough connectors. The pack also includes a 10A charger. I have to connect batteries into a logical unit of 24V/50Ah. It is fairly easy because Ping had instructed me very precisely through email.
I just made 2 trips around my small city with the new lifepo4 batteries. I saw that the wheelchair ran fine event while it climbed on slopes or moved 'off road', at least the same as lead acid batteries. And the speed is a bit higher. I estimate that this lifepo4 battery pack could serve for about 5 hours of continuous running or a range of 40-45km in maximum. I know that I should use 80% of its maximum to keep the batteries have a long life. So, 80% equals 4 hours of running or 35km, that's enough for me.
Conclusion:
40-45km is my desired range when I intended to move to lifepo4. It's about 2.5 times longer then lead acid batteries. Now, I can move to any where without to worry about the power. Although lifepo4 is now still expensive but I think it is worth for investing.
Caution:
Currently, I only try to move on short and low slopes. I have not tried to climb on ramp yet. My wheelchair is a light weight model, so it may only need a low concurrent discharging. If your wheelchair is a heavy model with stronger motors, you may need a bigger battery pack with higher concurrent discharging as Burgerman mentioned in the thread above.