Battery options for 36v 10ah?

[njmac]

Hi,
I'm new to the forum, having joined on behalf of my mum, who was given a Synergie Cruiser by a friend. The bike sat in a shed for a long tiem after a couple of wires had been pulled out. So my dad has sorted the wiring and the bike is alive again!
The battery is allowing my mum a brief jaunt but really needs replacing. A new 36V 10AH Lithium Ion Battery seems to be around £320, which is a bit scary.
I've been reading battery related posts and am now possibly more confused than when I started She won't be doing serious mileage so I think an alternative to the lithium ion could be feasible. I'm just not sure what the options are and what suppliers to speak to. Price will be a large part of the decision as the bike may not be used that often and paying over £300 for a battery, which will likely die in 2 years would be rather uneconomical.

Any advice greatly appreciated. I think this is the beastie in question by the way Synergie Bikes - Cruiser

cheers
nj

 

[NRG]

Well, you could go lead acid (SLA) but you will have to devise a way to mount them on the bike and connect them up....to get 36v you will need three very heavy batteries probably mounted atop the rack...not idea as it affects the handling but they are cheap. Or you could build your own Lithium battery but you'll need to really know what you are doing and somehow attend to low voltage cutoff and charging schemes or you could go to ping battery on Ebay and get a Lithium there....don't know if they are any cheaper than an original replacement though....

 

[daniel.weck]

If you don't mind taking the risk of shipping from China (and all the possible after-sales issues), you can get a long-lasting LiFePO4 battery for approximately 200 GBP:

36V 12AH LiFePO4 Battery Aluminium Case+ BMS+Charger on eBay (end time 26-Sep-10 10:26:31 BST)

36V 10AH LiFePO4 Battery Aluminium Case+BMS+Charger on eBay (end time 22-Sep-10 20:03:28 BST)

PS: I have picked this seller randomly, I have no idea whether they are a reliable firm.

 

[njmac]

Brilliant, thank you both for taking the time to post. I don't think the lead acid sounds like an ideal solution, especially as my mum's quite small and I on't see her taking the massive weight on the rack very well
But the LiFePO4 batteries are a definite possibility. I've bought quite a lot directly from china and for the most part I've had positive experiences. Are the LiFePO4 likely to be nearly as long lasting as the lithium?

I'll speak to the boss lady and see what she thinks
cheers
nj

 

[daniel.weck]

Are the LiFePO4 likely to be nearly as long lasting as the lithium?

LiFePO4 is a type of Lithium-Ion chemistry which allegedly lasts twice as long as say, LiPo or LiMn. For example, the rated number of charge cycles would be 500 for most Lithium-Ion batteries, whilst with LiFePO4 you're looking at 1000.

Now, this is all a bit theoretical because (1) there aren't many long-term reports from LiFePO4 owners yet and (2) it highly depends on discharge / charge patterns: high discharge rate (current draw) vs gentle use, battery recharge when reaching zero vs half capacity, cold storage when unused, etc. As a rule of thumb though, a LiFePO4 battery should last longer.

Other things to consider: LiFePO4 batteries are usually heavier, so they are less efficient in terms of capacity per weight density. They are somewhat also a little more expensive, although other battery chemistries of renowned manufacturing quality don't come cheap either - in which case you often get fewer charge cycles but higher reliable discharge rates (capacity to draw high currents continuously under load, useful for high-power applications).

I'm sure other (more knowledgeable) members will jump-in to concur or make corrections to what I said, as this is a recurrent subject in this forum. By the way, the search tool is actually pretty good, you should try searching for "lifepo4" to read more about the pros and cons.

Cheers, Dan

 

[NRG]

Nice one Dan, not seen those before.

Regarding life, yes, they are meant to give a long life but the quality of some cells coming out of China are a bit iffy and you could be unlucky and get a weak cell in the pack which will cause problems later...warranty may be non existant...what out for import duty as well

Batteries are the Achilles Heel of E-Bikes and I firmly believe that on the whole you get what you pay for, just MHO.

 

[njmac]

Aha, right I'm getting the idea now. I had previously searched and read many. many battery related posts but because i'm not overly familiar with specific bike models I wasn't sure whether some batteries suit specific models and riding styles better.
It's an interesting point regarding capacity per weight density. I imagine a small increase in weight can significantly reduce the effectiveness on a battery powered vehicle? Hopefully since my mum's only little that will offset the heavier battery if I go down that route Depends what she's just bought at M&S on the way home though.
I found this epic thread on an american site. The poster seems to have gone into some fine detail about the LiFePO4 he is testing (i think my thread on another forum covering the rebuild of an old audi was shorter). I have to say that at the end I still wasn't any wiser about buying one though because his review was specifically about the one he'd received.
Endless-sphere.com • View topic - E-Bikekit.com 36v 10ah LiFePo4 Battery

I know buying batteries from china can be touch and go but I know with other batteries (laptops etc) UK stock can often be the same units I would have bought from China. At least they have to be warrantied in the UK though yes?

I'll go and continue my research..
cheers
Nj

 

[daniel.weck]

LiFePO4 batteries from Li Ping (China) are famous for their reliability, and they come with a well-designed BMS (Battery Management System) to protect the cells.

PingBattery LiFePO4 Battery packs for Electric Bicycle e-Bike & Scooter, Lithium Iron Phosphate Battery

I use a 36V 10Ah battery from Li Ping and I am thoroughly happy with it. You should ask Li Ping if they can package cells inside your standard e-bike alloy box.