Storage of unused batteries - bonkas

Power System Futurology
1

I just destroyed my first lipo drone battery.
I think it happend becouse i stored it 3 month fully loadet.

I would always load the batteries direkt after flight soon as they are cooled handwarm.

Then lets say after some days (max. 3?) if i know that i will not fly the next day the batteries should be discharged to 50% i think

Bevore next use i have to top them all up.

If i had 12 bonkas that sounds like a lot of work, how would you do that?

And how importand is it to do that?

History of my first lipo drone battery:

I did about 50 flights with the now destroyed batterie,
Then i stored it full for about 2 month, did reload it and calibrated the drone, did wait 2 more weeks and flew first time after that long storageperiod.
Normal i got 9 minutes max. 11 minutes flight time.
That time just hovering around and much warmer than last flights the voltage warning kicked in after only 6 minutes flighttime.

The battery got puffed first time direkt after that flight.

Next day i could not close the door of the baterybox without cutting away some material.

I flew again and landet after 6 minutes to be on the save side but had some energy left but was definetly not good as it was bevore.

Direct after that flight the battery was puffed more and i had to cut again.

Then i flew a last time about 6 minutes and (maybe?) did not switch the drone off well, so it was active 6 more hours standby and drained the battery.

Then i could not start to load it 3 times, and as it startet it did never get complete full.

Puffed again more but looked good with motors running slow.

Next day i wantet to fly but seconds after start the voltage dropped to empty status.

Battery destroyed.

That one did cost me 100 $ but bonkas are way more expensive…

2

I believe you answered your own questions by example. Never store them full. The whole time they are full they are being stressed and getting damaged so it’s best to charge right before flight if you can. I charge mine the night before so I can fly when I get off work. Not the best practice though.

Storage charge is 3.8v per cell.

Don’t discharge below 3.5v. If you drop below 3.0v you will kill it. Note: it only takes seconds of flight to go from 3.5 to 3.0 so it’s not worth the flight time.

3

Thank you for the numbers

I heared that it is best to full load all batteries and then empty them to storage volt…

But i have no idea how to do it with 12 bonkas…

Does your loader offer a programm to discharge to 3,8 volts?

4

So do you load after flight to 3,8 volt

And the evening before flight just the rest to have them full the next day?

Think to let them empty after flight would damage them.

5

I’ve never heard that and I don’t know why that would ever make sense to do. Lipos don’t have a memory like some batteries do.

A charger can only discharge a battery by turning the power into heat. My charger would do it but it would take forever. I’d rather just fly to discharge.

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6

Christian,
Li-Ion and Li-Po batteries don’t like full charged state.
Storage at 100% for a few days is no problem, so charging the day before is also no problem. For longer periods is, as Paul already mentioned, a ‘storage state’ strongly advised, at least if you want to get some descent battery life. Yes, good chargers have storage settings in the menu. I store my batteries at 3,85V but anything between 3,8 and 3,9V is fine (both Li-Ion and Li-Po).
Many years ago, when the first low C-rated Li-Po batteries such as Kokam’s became available for hobby use they were very expensive, we had to threat them well.
Since these batteries became more available, cheaper and better, this rule became less important, at least for small(er) ‘heat shrink hose’ battery packs.
For larger packs and more expensive specific form made drone batteries it’s normal to still threat them as good as possible.
So besides the normal safety rules when (dis)charging, storage at ‘storage voltage’ is one rule.
Another one is to give the pack a good cool down after use before the next charge. I see you are aware of this so thumbs up.
Another one is to get the pack to room temperature before charging or discharging.
An important one for life expectancy is long time storage at lower temperature, during the winter period for example. I store mine in a closed moisture free fireproof box in the cellar.
The most important one for a descent life expectancy is to not charge them to 100% (if not necessary) and to not discharge them too low.
I personally charge my expensive packs to 4,10V max. A good charger has the possibility to set the charge termination voltage. If there 's only one Li-Po menu setting for 4,2V choose the Li-Ion menu setting of 4,1V. If you’re using HV Li-Po’s in future, use the 4,2V setting.
I discharge my expensive packs during flight to 3,5V/cell, a few short bursts of power to overcome an unexpected head wind is no problem.

If a battery puffs during charging terminate the charging process immediately and put the battery outside in a fireproof environment untill it is completely cooled down. Dispose it for recycling. Don’t use a puffed battery anymore, even if it’s only a little puffed. When it puffs further during use it can easily crack the housing/drone around it.

The explanation for this is simple.
It’s a known way to get batteries to their storage voltage when the charger in use has no storage voltage setting in the menu.
A normal charger always charges to ‘full’ and balances each cell individually almost at the end of the charging process.
It’s easier to start from a full battery and discharge afterwards by monitoring, to storage voltage, than terminating the charging process manually at the right moment.

Most of the chargers with a discharge mode discharge thru internal components, therefore discharge power is always very low, even with a built in fan. Also the more cells the battery has, the longer the discharging process takes:
Maximum dissipated power W is a constant and W = U (voltage) x I (current)
Higher end chargers sometimes have the possibility to connect an external load for discharging.
I prefer to simply use my charged batteries, and recharge them to storage level afterwards for storage. If I can not use them as proposed and want them to storage level, I hook them up to a dc charger and use them to charge other smaller batteries.
Regards.

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7

I have 2 sets of batteries. If one set is full and the other is empty and I know I won’t fly for a while then I will use the full ones to power my charger to charge the empty ones to storage level.

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8

@electriflyer and @gliderpilot
Thank you for the idea to use the full batteries for a dc to dc loader!
Thats a good idea not no waste the energy and get the full batteries down quick to the storage voltage if they was prepared but could not be used as planed!

1 Like
9

Has anyone had a bonka battery that went bad or expired early for some reason??? What’s their lifetime expectancy? I see comments about only charging to 80% and discharge to 3.5 but does that mean they last just a little bit longer? Do they have a lifetime of 1000 charges or so?

10

What is your definition of expired? Over time the batteries slowly lose capacity but still work. The rated life of a battery is considered over when the capacity drops to 80 percent… That just means shorter flight times but they still work.

They also slowly puff over time but still work. If they get too puffy it could be dangerous to continue to use them.

Discharging too low will completely kill the battery and you won’t be able to charge it again. When the cells get down to 3.5v you really only have a minute left to fly before the volts start dropping off fast. Is that minute of fun worth killing a battery? I don’t think so.

I have 2 sets of batteries. One set is a lot more puffy than the other. The second set I have taken better care of: charge to 4.15v, discharge to 3.5v with load, and always use 6 packs instead of 4 to keep the amp draw per pack lower and the temperature of the packs below 55C

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