Lithium batteries

[odaeio]

How good are li-po batteries really? Have been looking at the possibility of slowly replacing my lead-acids, but experience with my electric bicycle shows a tremendous difference between the advertising and reality.

Nearly all lithium batteries have a life of 5 to 7 thousand cycles, till they are down to 80% capacity - have only seen one that showed 3 to 5000.

My electric bike's battery has all the built in gubbins, each cell measured separately, disconnects before damaging dis-charge levels, proper charge monitoring and so on. The battery I got with the bike lasted just over 2 years, 700 cycles if used every day till flat, but I use it less than that, before it was down to 10% capacity. The second battery has lasted under 400 cycles and is now down to just under 50% capacity and dropping rapidly.

Should I be regarding the actual life cycle of Lithium's as around 10% of the advertised lies, in which case lead acid's are way, way cheaper, or do "proper" lithium's actually have anywhere near stated longevity? Do manufacturers like genuine A123 - as opposed to the Chinese counterfeit a123's - live up to their claims, or are all Lithium's just a load of bollocks?

Anyone got real life experience?

Have found 100 a/h "drop in" replacements at around £900.00 each - still to expensive, even if they do have a 20 year, (7000 cycle on daily use), life, but was considering building my own. (Could build them for around £500.00 per 100 a/h).

http://www.lithiumion-batteries.com/pro ... attery.php

The above, taken at their minimum cycle rate, would last under 10 years - at current prices I could replace my lead acid's every year and still have change - I currently get about 3 years to a set of lead acids before they become unusable.

I have 20 lead acids and cycle them around 25% discharge. After 3 or 4 month's they are down to about 50 % capacity, within a year they are down to about 30% capacity, and then they just sit there for the next two years or so, even though by that point I am cycling them at 95 to 100% discharge every day, due to their reduced capacity. I am on my 3rd set, so have seen this 3 times now and know what to expect out of a standard wet lead-acid "Leisure" battery. (The vast majority of boat batteries I have seen are down to under 30% capacity within 3 month's because the user cycles them 100% DOD before recharge - even though his daily use is only about 10% capacity, he just doesn't bother to charge till they are flat. Since he only needs 10% capacity anyway, his batteries "last" 2 or 3 years, so he will happily say he get's 5 years out of his batt's - especially if he is promoting some brand or the other. In reality his batt's are knackered within the first few month's, he just doesn't know it, because he has no need for the other 90% of supposedly available capacity. If his batteries actually worked properly, he would only need 1 small one instead of 5 huge ones!!!!!).

[adam2]

The main merit of lithium batteries is the much lighter weight for a given capacity, arguably worthwhile for electric cycles and portable electronics.

The claimed life time is seldom if ever realised in real world applications. The actual limit seems to be about 1,000 full cycles or a few years, whichever occurs first.

If weight is of little concern as for static applications then I would stick with lead acid, much cheaper and at least as long lasting in real world applications.

Lead acid batteries are also far safer, the contents are not flammable, explosive, nor under pressure.

Lithium cells are reasonably safe if correctly used, but are potentialy much less safe than lead acid under fault, failure or misuse conditions.

I have several hundred AH of lead acid batteries under my bed, certainly would not keep large lithium batteries under a bed ! and I am not too keen on keeping large lithium batteries indoors.

[odaeio]

Thanks Adam, lead acids it is again this time round. Same here, 10 x batt's under the couch and another 10 opposite under the cupboards - thermal runaway would be a rather large headache, although exciting!

How long do you think one could store "dry" lead acids? I may be coming into a bit of money at some point in the not too distant future, and was considering buying a hundred dry lead acids with the "pre-mix" electrolyte separately in plastic containers. Think this would keep for 10 to 15 years, or would the acid mix or plates deteriorate too fast anyway? Perhaps glass containers if the plastic would leach into the acid causing problems.

Idea is to only fill the batt's when replacement time come's around, hoping then to start the life of the battery. Storage would be a reasonably dry shed of some description, but wouldn't be temperature constant.

[adam2]

Not certain how long dry lead acids keep, but I would not count on longer than a year, two years at the very most.

Very large lead acid batteries are often shipped without acid, partly to reduce the weight. In such cases it is advised that the acid be added promptly after delivery. If this is not done, then the plates of the battery are liable to degradation from the air.

Small lead acid batteries as used in motorcycles are often supplied with acid in a seperate bottle, this somwhat extends the storage life since the battery is sealed to limit air ingress. It also eases international shipping since the battery may be sent from say China, and the acid supplied by a UK wholesaler or distributor.
I would not count on more than two years, and remember that is from manufacture, not from when you purchase the battery.

If planning for the long term, I would purchase good qaulity long lasting, conventional wet lead acid batteries. These should last 15 years with care.

For the still longer term the options come down to eather making your own lead acid cells, or use of nickle iron batteries.

[adam2]

Nickle iron batteries

http://www.powerswitch.org.uk/forum/vie ... hp?t=20181

[adam2]

Home made lead acid batteries
http://www.powerswitch.org.uk/forum/vie ... php?t=8367