How to determine when a LiPo Battery is DEAD

It’s known that like most things in life, LiPo batteries do not last forever. Eventually, LiPo batteries degrade to a point which makes them become unusable for your application.  The real question is, how do you know when an RC LiPo Battery is DEAD? Did you know that using a dead battery can actually be dangerous and could lead to catastrophic failure of the battery pack? A dead battery pack can also place extra strain on your ESC due to higher ripple voltages. If you are looking for more information on LiPo batteries it is recommended to check our LiPo batteries page.

Visual Inspection – When a LiPo Battery is DEAD

The most obvious way to determine if a LiPo battery is dead is to visually inspect it. What you are looking for when you are inspecting your LiPo battery pack is any sort of ballooning of the pack itself. A ballooning pack is caused when gases are released inside of the LiPo battery. Gases being released from a cell in a LiPo battery can happen for a number of reasons.

Generally, excessive heat is a contributor to packs that enlarge or balloon. If this happens to you during charging you must dispose of the pack immediately. You should dispose of the pack if this does happen at any time during use or no use. Ballooned LiPo battery packs can be very dangerous. 

How do you know a LiPo Battery is Dead?

How do you know a LiPo Battery is Dead?

Performance Test – When a LiPo Battery is DEAD

One of the easiest ways to determine if a LiPo battery pack is dead, is to review it’s performance characteristics.  This can be done by  placing the LiPo battery in the application that you intent to run the battery pack in. There are a few things to watch out for that would suggest your battery is around or past is expiry date. Let’s take a look.

Aggressive Run – Dead LiPo Test

The performance test  is quite simple and does not require much preparation other than a fully charged battery pack. What you will want to do is fully charge the battery and then place this in to your most power hungry vehicle that would of course use that battery pack.  You must be experienced running this vehicle to ensure that there are no power system concerns and everything has ran well before.

Run the battery pack more aggressively than you typically would. If your flying an airplane or driving a boat, maintain a higher average throttle setting than you typically would. If you are running an RC car accelerate more aggressively and frequently than you typically would. Keep in mind that if you are basing your run off a timer and you are driving more aggressively, you will burn more power. Don’t forget to consider this when setting your run time “timer.”

Only discharge the pack down to a maximum of 20%. Do not over discharge the pack as this won’t help or make your test any more conservative.

Once you have run your RC vehicle, these three items is what you should look for.

  1. Are you getting the expected performance out of your battery for the entire duration of your run?
  2. During the duration of the run, were there no low voltage cutoffs during the run?
  3. Is your battery operating at less than 60 degrees celcius or 140 degrees farenheit? (Dangerous if not)

If you have answered yes to these questions above, your pack is in fair condition. If you have answered no to any of the above questions, this could be a sign that your battery pack is in poor condition.

Looking at the Numbers – When a LiPo Battery is DEAD

If you have a more advanced charger, you may be able to use the information it offers to help you out. Take a look at your LiPo charger and see if it is possible for it to measure internal resistance often abbreviated IR. The unit of measurement is commonly in milli-ohms. (m Ω)

To use the resistance value determined by our charger, we first need to start with a discharged battery and use the charge function. Or you may start with a fully charged battery and use the discharge function. Discharging a pack to get a resistance reading is only recommended if your charger can discharge a significant amount of power.

It’s highly recommended to use the resistance determined by the charger during a charge cycle as you will be charging the battery regularly presumably. It’s also best to know the internal resistance of your packs cells when you purchased them new.  Determine the internal resistance  by charging your LiPo batteries and recording the internal resistance computed by your charger.

Measuring RC LiPo cell internal resistance (IR)

Measuring RC LiPo cell internal resistance (IR)

Once you have charged your pack and record the internal resistance you can determine the health of the cells in your LiPo battery pack. Generally speaking, if the resistance goes up by 2-3 times the original amount, your LiPo cells are suffering in performance. Depending on the application these packs are used in, 2-3 times the internal resistance may make them completely useless.

If you don’t know the internal resistance per cell of your LiPo pack when purchased new, here is a quick reference chart. Keep in mind these values are general values.

 

C Rating Capacity (mAh) IR per Cell (m Ω)
30 850 20
30 5000 2.9
45 2200 6.5
45 2200 2.6
65 1200 9.2
65 5000 1.9

Conclusion – When a LiPo Battery is DEAD

The method I typically use is actually a combination of the above.  If I’m happy using a half dead LiPo in an application that allows it, even with the weaker performance / capacity, then so be it.  As long as the LiPo is not in a dangerous state.When I can no longer use the LiPo battery pack, it is disposed of accordingly and a replacement is purchased.

 

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