EV Batteries, How to look after them.

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  • #118204 Reply

    OK, so you’re worried about horror stories where someone has had a BEV for a few years and the battery is down to 50% of it’s capacity due to that awful battery degradation. So, what’s the story and how do you avoid this happening to you?

    Modern BEVs come with a “lithium” battery pack, made up of lots of individual cells into groups of cells that with a Battery Management System (BMS) and cooling/heating tubes go together to make that very large battery hanging underneath the car.

    The batteries, they’re almost certainly “lithium ion”, and these come in different “flavours”: metal-oxides (e.g. Lithium Manganese Oxide, LiMn2O2), or phosphates (e.g. Lithium Iron Phosphate, LiFePO4). The phosphates are preferable in BEVs as they’re much safer and have relatively long lives.

    So, we have the batteries, they’re safe, but they still need looking after, if they run too hot or too cold they won’t work properly, hence the need for heating and cooling, liquid cooled (antifreeze) in some, air cooled in others, and not much at all in others due to battery capacity being increased without regard to increased heat generation (thankyou Nissan). Air cooling has fans and air ducts. Water cooling & possibly heating has pipework and often a heat exchange system (and you thought that heat pump was for your comfort in the cabin?).

    That leaves the BMS, the Battery Management System or Battery Mismanagement System in some BEVs. This consists of some electronics and a lot of cables, plus links to the cooling/heating system.

    Remember you have lots of smaller battery cells making up modules and modules making up the whole battery. When you charge the BEV it starts off with the BULK CHARGE, this can be delivered at very high rates using a DC Rapid charger, but after the battery reaches a higher state of charge some of those individual battery cells will have more electricity stored away in them than others…. that’s where the BMS comes in, to “balance” the cells. The balancing process involves all those finer cables in the battery pack, they allow the thicker cables to charge the battery whilst the finer cables are  used to drop or leak individual cell voltages down to stop them getting damaged whilst others are still charging full rate.

    So, how do we get around this slowing down of the charging? Well, we don’t really, we leave the Rapid charger when we have about 80% charge & continue our journey. When we reach our destination we plug into the AC fast charge post or plug it into our wallbox and use these to “balance” the battery cells over a longer time (overnight full charge once a week should do it). If the battery pack doesn’t get that occasional full balance charge then it will degrade much faster.

    In addition the BMS can limit the power available whilst driving, this is what you see when the BEV uses “modes”, Eco limits the power available using the BMS, Sport gives the full amount allowed by the BMS, speeds are limited again by the BMS. If you run short of electricty then you’ll see “Turtle Mode” and the BMS progressively limiting the power whilst you get nagged to recharge as soon as possible. Go beyond Turtle Mode and the car will stop & shut down to stop you from draining the battery completely which kills it forever.

    So, keep your battery between 10% and 80% whilst using the car if you can, and charge it to 100% once a week just before you use the car. If you’re leaving the car unused for a while, aim for 60-70% charge level, that’s where the lithium batteries are happy, unlike lead acid batteries which degrade unless they’re at 100%.


    If a battery is too cold it won’t charge rapidly, it’ll throttle the charge rate. Some cars will heat the battery pack in cold conditions to help, some will just charge very slowly (coldgate).

    If a battery is too hot it will be damaged by charging rapidly or by driving (remember high regen rates going down hills), to counter this in warmer weather some cars will cool the battery pack whilst charging and sometimes whilst driving, they will also throttle the rapid charge rates (rapidgate).


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  • #118210 Reply

    Going to a pump is a lot less hassle it seems. I look and see a green label  when i open the cover, I have mental health and memory problems. so how will i rememeber all this info and how i charged up the car last time..

    It’s the same with mobile phones and sometimes they just bad batteries from the start, I had one on my golf mk7 after a few months of having the car it had to be replaced by the Rac. In many years of driving on the scheme thats the only thing that has left me stranded a faulty battery.

    #118214 Reply

    In many years of driving on the scheme thats the only thing that has left me stranded a faulty battery.

    Strangely on BEV cars it’s usually the 12v lead acid battery that also causes the breakdowns, it’s needed to run the display electronics, windows, central locking, etc., and there have been many instances of this battery going bad because the BEV logic didn’t remember to charge the legacy 12V battery, & no-one thought to have it charged to 100% by the end of every journey as you would on a fossil car, so they degrade the lead acid battery very fast. Two solutions, better legacy battery management by the BEVs “brains”, or, install a lithium legacy replacement battery which won’t mind being left at a lower state of charge.

    The plan for my own BEV is to pull out the legacy 12V battery & substitute a bank of LiFePO4 cells that I happen to have 80 of laying around unused, there’s no starter motor to worry about cold cranking amps, and I can cram in a larger capacity in terms of ampere hours into the same space. This is for auxillary electrics, not for traction.

    #118223 Reply

    “The plan for my own BEV is to pull out the legacy 12V battery & substitute a bank of LiFePO4 cells that I happen to have 80 of laying around unused.” Obviously you wouldn’t put these in a Motability car.

    #118234 Reply

    Great info as always, It’s deffo intresting times, I saw some vids a while ago about running cars on water and creating hydrogen via electrolysis and putting it directly into the combustion chamber, but i think that tech will never be pushed or allowed to become mainstream. Because they need to make money from it all..

    I do believe even if the cost of bev’s come down and ranges get better and fossil fuels end, They will need to find the cash somewhere. As they going to lose alot of revenue from ice cars and the tax on fuel.. or other energy creation and use not deemed green. They’ll probally have a it a congestion charge / pay per mile and price the poor off the roads.

    Plus the same few will profit hugely from the uptake of certain technologys over others as always and electric technology was surpressed for years before it became the new gold rush, The oil could well be running out?  Solar farms are popping up in fields near me at an alarming rates and everything comes at a cost even generating electric, That a lot don’t see or count or care about. Nothing is done imo to benefit the ppl only to charge us for it and keep us in debt and thus enslaved to pay it back.

    After all the UN say’s the people must pay for the demise of the car.

    At first though they dangle the carrot and get you hooked. Then it just get higher and higher and it won’t be worth owning a car or they won’t even allow it. In london they removing the exemption for resident from the congestion charge from 1st of aug to discourage them from owning cars. which is what i don’t agree with. Which they extending to nc. and sc. roads soon. Then it will be changed and changed until you cannot own a car at all any where in london.

    In paris the scheme is different totally you pay for a sticker to say your car is emission friendly and it costs around 3 euros p+p and thats it.. for as long as you can read the details. So the car is deffo being used as a cash cow in the uk and where will the money come from when we go more and more towards zero emissions.



    #118240 Reply

    “The plan for my own BEV is to pull out the legacy 12V battery & substitute a bank of LiFePO4 cells that I happen to have 80 of laying around unused.” Obviously you wouldn’t put these in a Motability car.

    Obviously not, if the car kept breaking down because the 12V battery was flat you’d reject the car & choose a different one, after all it’s a clear design fault, even if the fix is trivially simple. So simple the MG ZS EV even has a button to recharge the 12V battery manually.

    However, 4 x 15Ah cells to make the 12V, that would be a tiny but reliable battery that weighs about 1/4 the 12 lead acid battery, that means a little extra range, that’s why you’d do it to a motability car. Or just eat 1 less pie a month.


    #118247 Reply

    lol Smallcar you could also drive around with o few of these on as well ha ha.

    #130282 Reply

    Hyundai Kona, BMS related recall



    Fires because the BMS (Battery Management System) hasn’t been protecting the lithium ion cells properly during (rapid) charging.

    Trouble here is that BMS problems have been endemic with lithium batteries since people started using a BMS, & each new battery engineer seems to make the same old mistakes, usually the one where the balance leads can’t carry a high enough current to drop the over-voltage cells enough whilst the rest catch up, or, the circuit board can’t cope for the same reason, this time it seems the logic (ROM) is flawed.



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