To answer this question we discuss basics LIPO batteries and the reasons for discharging batteries after use.
If you have been in this hobby for any length of time your first rechargeable battery was either a NiCad or NiMH battery. More recently LIPO batteries have replaced the need for NiMH packs but many are still unaware that LIPO batteries need to be cared for to get the most from them. You could run NiMh packs until they were completely dead, sucking every last drop out of your pack without as much as blinking an eye. It probably wasn’t good for them but those packs didn’t seem to mind. You could put them back on charge and use them again with callous disregard. In fact, I remember being told that you had to fully charge and discharge NiCads to avoid the memory effect. Nimhs didn’t have a memory in the same way and they were much more desirable. The Nimh packs also had a larger capacity and could be charged faster.
NiMh packs would take forever to charge and the packs were worth a fortune. LiPo batteries changed all this as they were a lot cheaper and much more powerful. Electric planes and helicopters existed with NiMH packs but they weren’t exciting. Gliders and smaller helicopters were lacklustre. LIPO’s changed all that and in a relatively short period of time. Couple that with powerful brushless motors and it’s no wonder that internal combustion motors went the way of the dinosaurs. Well not quite, but, it’s not far off. There are still IC engines but few and far between. They are dirty, smelly, bothersome and tedious most of the time, plus your model is covered in oil after a run.
LIPO batteries are able to supply massive amounts of current whenever we push the throttle forward. Every Modern LIPO battery can be charged quickly and some even 10 or 15C. This equates to a charge time under 10 minutes. The tradeoff is that LIPOS must be handled and stored with care. They are volatile and if treated poorly can burst into flames. This is why a good charger is a must as is proper battery care and handling. They should not be left fully charged state for extended periods as it degrades the battery, but also this is when the battery is at its most volatile. If a flat battery is punctured little happens. Perhaps a little smoke is released but a fully charged or overcharged battery is at its most dangerous.
This battery has been overcharged intentionally.
Batteries don’t exactly store energy. When you recharge a battery you are reversing a chemical reaction. By definition, A rechargeable battery is a battery that can be recharged and discharged many times over. Charging and discharging batteries involve redox chemistry. Discharging a battery involves the conversion of chemical energy to electrical energy. It is this chemical energy that is volatile. Leaving the battery fully charged degrades the ability for the chemical reaction to take place. Not only will the performance be reduced but also the capacity. Internal resistance is the main measurement used to assess battery integrity/capability and anyone who has left a battery inadvertently charged for an extended period will tell you that IR rises dramatically. This is not reversible and this damage is permanent.
What is Storage Voltage?
A LiPo battery pack should be stored at approximately 30% to 40% of its stated capacity, then placed in a LiPo battery bag/sack and stored in a cool dry area away from anything that could potentially catch fire in the event that the battery had a catastrophic failure. Check the LiPo battery pack regularly during long-term storage. Once every two months should be sufficient and if necessary you should top the battery up to ensure the battery is at 30-40%.
LIPO batteries must be handled and stored differently than other chemistries and this is because they are more volatile. We can extend the usable service life of the battery by taking care of the battery properly. The key to this is ensuring the battery is stored between 3.7-3.8v and that the battery is stored in a cool place. Most modern LIPO battery chargers are equipped with a LiPo storage function that will either charge or discharge the battery depending on the starting voltage. I suggest you place your LIPO batteries in storage mode as quickly as possible. Get into the habit of looking after your batteries because not only is it safer to do so but you’ll save money.
If you have not already invested in fireproof containers now is a good time to do so. As I mentioned above, LIPO batteries are volatile and can ignite if damaged or stressed. Most people use products such as LIPO bags, battery boxes or even used ammo boxes from disposal stores. LIPO bags are cheap and readily available and hopefully, they stop damage to your property in the event that something did go wrong. I have also read that some have used ceramic flower pots however this is a terrible idea. If a battery were to ignite there is an incredible amount of thermal energy that is released. This is sure to crack a ceramic vessel and fail to contain a fire.
By taking care of your batteries you will extend their life and reduce the chance of cell damage. In addition, you’ll reduce the risk of fire and damage to your property. Modern chargers are able to take your batteries down to storage voltage to make life easier for you. Get into the habit of caring for your batteries as they are neither cheap nor forgiving. If you’re about to purchase a new charger the make sure it has storage mode.
Best of Luck and Happy Landings