AGM BATTERY V LITHIUM

[woodman-46]

I have already posted a question about putting AGM batteries together in a case/box and had some really helpful answers. I have another question about the batteries themselves and wanted to put it as a separate thread.
I am converting a small motorbike for my young son to electric from petrol and it will be powered by a 48v 800w hub motor. I have been tossing up between agm batteries and lithium. Agm ones are fairly cheap ,safe but fairly heavy (16kg for four 12v) Lithium are expensive , light but have been known to catch fire. Lithium have a pretty long life and a lot of charging cycles. I am actually more keen on using deep cycle AGM batteries for a number of reasons but can anyone tell me how "efficient" they are. I have been told that a 15ah one will lose power fairly quickly and that after a while just go down to 50% whereas lithium will go on on a good power until it has no charge and then stop suddenly. Can anyone let me know about the efficiency of AGM batteries and any experience with them and whether they would work for me. Thanks

 

[stillp]

lithium will go on on a good power until it has no charge and then stop suddenly

That's normally done by electronics in the device switching off before the battery is completely flat. If you run a lithium battery completely flat it will never work again.

 

[Keithmac]

I would go Lithium Ion, a proper pack with built in controller.

Discharge a Lithium pack below a certain voltage and it's scrap, the controller will turn it off before this voltage.

AGM are cheaper but a lot heavier, not as good at charge cycling and performance drops off as they discharge.

 

[ericmark]

I have a camera with a lithium battery special designed for camera likely with some software in the case and they can sit in the camera for 6 months and still work. However I also have AA cells and some will lose the charge rather fast, really need charging on day of use.

The same maybe to a smaller extent is true with valve regulated lead acid.

I would say the main problem is the charger, in both cases, look at a VRLA in a stair lift and lucky to get two years, yet in a mobility scooter can easy last ten, but the stair lift charger is fixed voltage of around 13.8 to 14 volt per 12 volt battery and the mobility scooter uses a three stage charger with final top up at 13.2 volt.

If you can for example get the batteries out of a wheel charge, mobility scooter, electric bike together with all the software which controls their charging then likely the lithium will be best, but if you need to design your own charging method the VRLA is the way to go as far easier to get a good stage or pulse charger which will not damage the batteries.

 

[Keithmac]

Have a good read up on endless-sphere.com .

I personally wouldn't entertain LiPo packs due to the careful handling and charging required.

 

[woodman-46]

Thanks for your help and advice.

 

[gblades]

If you want to go Lithium then go for LFP (LiFePO4). They are a lot safer and have a slightly lower 3.2V normal voltage over the majority of their discharge which means 4 cells gives 12.8V which is handy when using them to replace AGM batteries.
You might find this of interest

 

[ericmark]

That's normally done by electronics in the device switching off before the battery is completely flat. If you run a lithium battery completely flat it will never work again.

I had not realised this, with acid batteries one stored fully charged and with alkaline batteries one stored fully discharged. That was in days of lead acid and Ni/iron when the dry cell Ni/Cad battery came out it was stored discharged after manufacturer, but one it was charged then crystals could form so it was kept charged as when charged any crystal would be burnt away as it formed, but when discharged the crystal growth would short out the battery stopping it being recharged, one trick often done was to put a faulty battery is parallel with a good one which could burn the crystal but it could also cause the battery to explode.

When the lithium battery arrived is seems there were many versions, so would come from the manufacturer discharged others would come part charged. I know my camera battery has been allowed to become fully discharged when the camera was not used for over a year, and it recharged without a problem. However other items left have when come back to had a battery which had swelled up and clearly faulty.

Quick look

• Lithium ion manganese oxide battery
• Lithium iron phosphate battery
• Lithium polymer battery
• Lithium sulfur battery
• Lithium titanate battery
• Lithium vanadium phosphate battery
• Lithium-ion flow battery
• Lithium–air battery
• Lithium–silicon battery

It would seem there are many Lithium batteries I suppose there are also many lead acid types, but a stage charger seems reasonably standard for all lead acid types, where with Lithium

often the charge controller is built into the battery as there are so many types.

I use Lithium batteries to work phones and cameras and it clearly has a lot of electronics built in, as output is 5 volt but also charged from 5 volt. I am sure some one can expand on all the different Lithium batteries, however for what is wanted here it would seem they are unknown this battery is 3.85 Ah at £137 I am sure there are some applications that need it, but I think I would play safe and use lead acid!

 

[ban-all-sheds]

There are also lithium primary batteries....