I've been riding to work every day this week - 29ks return and I JUST make it off a single charge from the 8ah pack so I'm pretty happy with that. I was intially charging at work but after my 2nd charger (one of THESE ) died after only 4 charges I had to risk the return trip on a single charge. Luckily the shop I got it from gave me a full refund so I can now go done a more gangsta path
I've been speaking with methods and am going to make up something similar to what he's doing with his high powered onboard charger, but on a smaller scale of course. I'm going to get THIS 24v 6a power supply. It has a +/-10% variable output, so I'll set it to 25.2v and pour 6 amps into my 4 6s 4000ah lipos packs in parallel. That's around 1.5a each which is under 1/2C so should be nice and safe and hopefully I'll get the most life from the batteries. The manufacturer recommends charging at 1a and 2a max which seems pretty low, but I dont want to be too daring with high current charge rates on these cheap no name packs given I often charge them indoors. Besides, a charge time of 2.5-3hrs is quite acceptable for my needs.
The only problem now is I think I need a better bike, or atleast suspension!
Travelling at 30-40km/hr along sections of bumpy footpaths and crappy access roads along the side of the highway on the way to work makes for a bone jarring ride! It's only a cheap bke so I can't expect too much, but I dunno if upgrading the front shocks alone will make it much better. If I have to replace too much it might be easier to get a better new bike. Either that or up the voltage some more so I can keep up with the cars and ride on the road
(I have a Original B&S Etek and a Alltrax 48 Volt 300 Amp controller...this could be a way to make so use of them again that white shit we get )
I'd like to build something totally custom like Hal is but I havent got the skill or cash, but I reckon if I was to cut the full length of the bottom bar of the frame in half and weld on a piece of rectangular channel I could easily hide 44v 8ah worth lipos in there. OR, I could cut that bar away completely and replace it with a wider longer section and just weld to the other bits of the frame which would be neater, but then I'd be more fiddley around the bottom bracket etc and I'm sure I'd botch it up!
Browsing ebay I thought I'd probably get an ecrazyman controller but found a local seller just up the road from me selling whole kits. I emailed and asked if they sold spare controllers seperately which they did and to my delight $50 later ($35 US) I had a big fat "36v 1000w" controller in my lap. I was also pleased to find it took my 50v hot off the charge lipo pack straight out of the box, so no need to mod it. $2 worth of duct tape later its on the bike and up the street for a test run, still with no crank. I dont know if its this controller or the throttle or what, but the acceleration is alot different to my GM one. It seems to accelerate fairly gently and smoothly to about 30km/hr and then levels out like thats all its got, but then open the throttle right up and it launches off. It has much more top end torque than my GM and clocked 44km/hr on the flat (GPS) vs about 39km/hr on the same pack for the GM. So very pleased with this I'm back to the workshop to get the watts up meter and see what sort current it's pulling. Cruising along its doing 10-15-20 amps, much the same as my GM, then I opened it up and looked down to see 42 amps! Damn, that's where the extra torque is coming from! Sadly my cheap 8ah lipos didnt like this and the voltage quickly sagged. 
