How to gauge safety of cheap Lipo batteries?

I see a ton of cheap 12V lipo batteries for sale on Ebay, but other than the mAh rating, I can't find any info or datasheets on how to safely operate them. I'm looking for a good battery to power a couple of small gear motors, so I'd like to know the maximum safe continuous discharge rate. I've emailed several of these retailers, which all seem to be based in China, and everyone one of them has basically said, "sorry, we don't know". These batteries are interesting in that they include a compact built-in charging circuit, and I'm no where near confident enough to design my own. However, the lack of documentation makes me nervous.

Are these cheap Chinese batteries junk, or can they be used safely? Is there somewhere that provides a basic datasheet for them?

A lot of guides I've read on how to safely use lipo batteries read like you're handling a bomb that might explode at any moment. e.g. "never leave unattended" and "always store in a fireproof container". Are these concerns still justified? A lot of cellphones and laptops include these batteries and don't come with similar warnings. I just don't want to plug in one of these Chinese batteries to charge overnight and wake-up to a house fire.

• 12V is not a voltage LiPo batteries are rated for, either nominally or fully-charged. That in itself is a black mark. – Ignacio Vazquez-Abrams Mar 24 '15 at 15:43
• Oh you won't wake up in a house fire... or at all... – PlasmaHH Mar 24 '15 at 15:44
• @RogerRowland, Please don't be rude. – Cerin Mar 24 '15 at 16:04
• @IgnacioVazquez-Abrams, Batteries, especially lipos, are often combined in series to form a larger voltage... – Cerin Mar 24 '15 at 16:06
• @Cerin Ahhhh ... you misunderstand, I'm sorry. When I said "Stupid comment #1", I was referring to my comment, in the sense that "this may be obvious, but...". It was not intented to be meant for you. Please accept my apology for the confusion, and have an upvote. I will remove my first comment. – Roger Rowland Mar 24 '15 at 16:14

I have randomly purchased several of these relatively cheap lithium ion batteries from ebay, originating from China. I have a fairly high quality battery charger/analyzer that I use to test these batteries.

They have all been the advertised voltage, but he capacity is nowhere near what they claim. A 5000 mAh battery tested at 333maH. Another 5000 mAh (claimed 5000 mAh) battery came in at 571 mAh. Clearly these inexpensive batteries are closer to 1/10 the claimed capcity. I have managed to get a refund when I complained to the seller.

I saw a video on YouTube where a person took an 18650 battery bought off of ebay from China (that had a tested capacity significantly lower than claimed) and he took the battery apart. Inside was a minature battery that looked like a triple 'A' battery surrounded by a powder that looked like flour!

In other words you get what you pay for. From my experience, it appears as though batteries manufactured in Japan tend to be of higher quality/capacity, although that can change quickly. If the battery you are looking at has a 'C' and mAh rating, then you might be able to get a refund from ebay if the battery doesn't perform as advertised. Today's lithium batteries appear to be relatively safe as long as you don't use them beyond the abilities or 'C' rating. Fire proof boxes are not necessary for storage, but recommendations from manufacturers still tend to include the instruction to "not leave the battery charging unattended". I suspect that this has to do with the fact that there are a lot of really cheap and poorly made chargers that potentially slightly overcharge the battery (usually through trickle charging which you should not do with lithium ion) which is what leads to fires and explosions.

LiPo's are usually rated by a discharge value "C". This is capacity multiplied by the C value.

For example, a 11.1V 5C 1000mAh battery:

5 x 1000mAh = 5000mA or 5A discharge

You should be able to draw at-least 1C safely from most lithium batteries. Check the eBay listing again to see if they include a C value, it might be there.

I always try to order batteries which include a C value in the listing, now whether or not the listing is accurate is a different story..

• I'm aware of the C rating. I agree, that's exactly what I need, but none of the listings I can find mention it. I explicitly asked several of the sellers for this, and none could provide it. – Cerin Mar 24 '15 at 16:15
• @Cerin Most of the sellers don't even know what a battery is. They just get handed a catalog of items by the Chinese distributors and orders for them get forwarded to a distribution point. The sellers don't often have the actual items themselves, they just act as agents for an anonymous reseller in China. If you look, they all sell the exact same range of bizarre, unrelated, crud. Also they may quote one day delivery, but if you read the small print you see that orders will be processed in 5 days or more - to give the international shipment time to get there. – Majenko Mar 24 '15 at 16:27
• @Cerin from my experience with the cheap eBay batteries.. they often have mislabeled capacities and sent in improper packaging. I wouldn't trust the quality... spend the extra  an buy from a reputable source. – Colin G Mar 24 '15 at 17:56

Having their own charging circuit is a good sign, especially if it includes a thermistor. Probably the best way to assess it is to charge it once under a careful eye while monitoring current and voltage. It should have a constant current charge up to its nominal voltage of ~4.2V per cell then constant voltage with diminishing current, then finally turn off (not trickle charge). During this process it should not get too hot (body temperature is about right, 50C absolute max in 20C ambient).

R/C batteries can put out high current and tend not to have protective current limiters. This means that shorting them out can ignite them. Puncturing the battery can give you an unextinguishable fire. But just leaving them lying around is not going to spontaneously explode.

• Batteries are perfectly safe without a built in charging circuit. I'd argue buying a cheap battery that claims it has a charging circuit built in would be less safe than just a plain battery. At least you know your charging circuit is safe if you designed it. – ACD Mar 24 '15 at 16:53