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How to Tell If Your Lipo Battery Is Good

LIPO batteries are found in just about every modern convenience these days and whilst we don’t pay much attention to them we really should. Proper care dramatically extends their usable lifespan and given batteries are so expensive its worth looking after them so that they give you reliable service for years to come.

Your LIPO battery not only provides power to your motor but also the receiver and servo controls. If your battery fails you’re going to have a bad day and it’s not only the loss of the model but damage to property or people. Although LIPO technology has come along in leaps and bounds in the last decade we should not take them for granted. You’re probably thinking; I don’t worry about my phone battery or iPad battery so why worry about the LIPOS in our RC gear. We know that our batteries share a common chemistry with consumer grade electronics however that’s where the similarities end. Consumer grade LIPO batteries are generally not user serviceable and the health and charging are handled by sophisticated hardware and software. Although we have tools at our disposal we often don’t use them. It is however up to you to determine the battery health and flight worthiness.

What is a good LIPO battery?

A good LIPO battery is one that gives you reliability and a good service life. It will retain a good portion of its capacity even after 300 cycles. It will be capable of producing close to its rated amperage output without damaging the battery. It will have the same capacity and a very low internal resistance across all cells. You will be able to immediately charge the battery after use and return to service immediately after charge. There is a reason that so many people trust Turnigy, Flightmax, Nano-tech and the industry gold standard, Turnigy Graphene Packs.

Most LIPO batteries should give you between 2 and 4 years of service provided you take care of the pack.

  • Store your LIPO battery above 4DegC and below 22DegC when not in use.
  • Store your LIPO battery between 3.7v and 3.85v when not in use.
  • Never leave your battery fully charged for longer than 24 hours.
  • Never use a LOW C battery in a HIGH C application.
  • Never use more than 80% of the pack capacity
  • Never allow the battery to be completely discharged as this will permanently and irreversibly damage the battery.

What Does a Bad Battery Look Like?

A pack should feel firm and not be bulged or puffed. Whilst a little swelling after use is ok (no idea) a clearly puffed pack should be disposed of. Before you blame the manufacturer for yourself… Is this battery suitable for my application? For example, running a 25C pack in a Jet or high-performance aircraft. You’re going to be very disappointed and the pack will have a very short life. If you find that only one cell is puffed. This is indicative of a cell that is on the way out so keep your eye on it. If the cell begins to swell further, cell IR increases, cell capacity reduces or is much warmer after use compared to the neighbouring cells then dispose of the battery. A battery is often a lot cheaper than a new model so think twice.

If you use a hard case packs such as the ones in cars or boats, check for broken terminals, a crack or bulge in the plastic case or where the black plastic case has turned white from stress. If your battery has a loose terminal you need to fix the issue with epoxy or retire from service. If that terminal comes loose inside the pack it has the potential cause a short circuit. LIPO batteries are able to dump massive amounts of current very quickly and this will almost certainly result in a fire. LIPO fires do not require oxygen to burn.

A lipo battery is only as good as the weakest cell. If you have a LIPO battery with a dodgy cell you’re running a massive risk of failure. There are no user serviceable parts in a battery so once you’ve determined there is a faulty cell take it out of your circulation.

What To buy

Buy reliable packs that are well known to the community and steer clear of no-name fly-by-night operators. You will do yourself no favours and it’s a trap for noobs. Smaller operators get B-Grade packs as they order is small quantities. Be careful of dubious claims from the smaller operators. Turnigy Graphene is arguably the best pack on the market today and yet they are still at 65C. How is it possible that we see packs at 100C – 150C or even greater. This is indeed little more than the hustle and something to keep an eye out for.

Battery Reviewers- Who to Believe?

A review must be scientific to be of any value. A review that talks about how it looks and feels to the touch are worthless. Show me the numbers!!! amps, watts, volts from a reputable trusted source.

This young man looks quite foolish in this “teardown review”. It is a little sad that some of the comments appear to be equally as ignorant. Unfortunately, nobody told him that graphene cannot be seen by the naked eye. Opening a LIPO battery and making a profound statement that the battery has no Graphene is ridiculous.

LIPO Battery Cell Voltages

We can learn a lot about the health of the battery by looking at the individual cell voltages. Each cell should be as close as possible to each other. This must be determined by testing with a multimeter, as a charged should only be considered indicative at best.

  • Acceptable variance (low end) 3.85 3.85 3.84 (high end) 4.19 4.20 4.19

So how does cell voltage determine health? As a LIPO is discharged the voltage in the cell drops. 4.20v is considered to be fully charged and 3.00v is considered completely discharged. When current is drawn from the battery the voltage drops. Obviously the smaller the capacity the faster the current will drop. As the cell deteriorates the capacity of the cell is will often be reduced and this can be observed in variances in cell voltage. Although you have charged the battery to 4.20v per cell at the completion of the run or flight the battery cell voltages may show a high variance. 3.85 3.85 3.61. In this example, the capacity of cell 3 is significantly reduced and should be retired. The battery cannot be rejuvenated or repaired.

Use a Quality LIPO Charger

Using a good LIPO charger is essential to keeping your packs in good health. LIPO batteries are volatile so it’s important to use a highly accurate unit. Overcharging a LIPO will cause damage to the battery and can result in a fire so this is one area where it’s truly an investment.

You must be able to trust the charger and provided you invest in a good charger you’re going to have it for years. Even though your interests in the hobby may change your charger should still be able to charge any number of cell types and configurations. Chargers range in cost from $5 for an entry level no frills unit to a top of the line 10S 30amps charger for $300+.

If you want a trusted unit that is affordable most people use the Turnigy Accucel 6. Modellers the world over use the Accucel6 because its lowcost, reliable, and still a quality unit. Whilst it lacks the options of the bigger units it still packs a punch.

If you’re looking to invest in an excellent charger then the Turnigy Reaktor line is worth considering. High-quality high output chargers are not cheap however they are the best.

It important to know how many watts or amps your system is drawing?

Your electrical system has a limit that should not be exceeded. As you exceed the limit of your electrical system heat is generated and resistance increases, as resistance increases so does heat, until you let all the magic smoke out. At this point you regret not using a watt meter and you fork out for a new motor, ESC or battery. Different loads can have a massive impact on current draw. Going from a 3s battery to a 4s is a good example where a wattmeter is critically important. Get into a habit of using it so that you can avoid damaging your power system.

By ensuring your battery is not stressed you will have the best chance of getting the most from that pack. Take the time to look after your battery and you’ll get a great serviceable life from them.

Happy Landings.

Written by Gozarian


 

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