The Safety Technology Authority (TUKES) has examined the safety of the mobile phone lithium-ion (Li Ion) replacement batteries on the market in Finland. We found no further battery models that could be classified as dangerous. Instead, the tests in which the batteries were forced to explode showed further safety improvement needs for many battery models.

The safety problems of replacement batteries came out last year, when there were consumer reports on explosions of lithium-ion replacement batteries suitable for Nokia 3310 and 3330. The products were not original Nokia parts but replacements manufactured by others. The battery lots that had caused the hazardous situations were recalled from the market.

The explosions were due to an internal short-circuit occurred in the battery cell. The short-circuiting may have arisen e.g. after the phone had been dropped or even without any outside reason. After the short-circuit, the battery had become very warm and bulged, and in some cases even exploded.

By way of examining the safety of replacement batteries, we purchased a variety of batteries from 14 importers and had them tested by the SGS Fimko Oy laboratory. All the examined batteries were suitable for Nokia models 3310, 3330, 3390, 3410, 3510, 6800 and 6650, so they were of the same size as those exploded when used by consumers.

Totally 54 batteries underwent a test where the laboratory intentionally tried to cause an internal short-circuit in the battery cell by damaging them in drop tests and by causing external short-circuits in the cell in the absence of the battery's protection circuit. These tests, where the conditions were much harder than in normal use, no battery could be made to explode.

As we wanted to know, how the batteries react in an explosion, additional tests were carried out where the batteries were forced to explode by heating them heavily from outside. The batteries that lacked an overpressure relief valve in the cell casing exploded with strong damaging effect. In some cases the parts blown up in the explosion caught fire. On the other hand, the batteries whose cell had the relief valve did not actually explode, but the overpressure was discharged heavily without breaking the cell casing.

The international safety standard IEC 61960-2 applying to Li-Ion batteries does not require any relief valve in the battery cell. The non-explosion of the batteries shall be assured by means of the tests referred to in the standard. Of the 19 replacement battery models tested by TUKES, five had the relief valve, although it is not required. We think a relief valve with reliable functioning improves the safety.

TUKES still welcomes consumer and company notifications on possible hazardous situations caused by batteries – which can easily be made on our website.

Examples of safety vents on gsm accumulator Li-ion cells

For further information:
Kari Lehto, Senior Safety Engineer, tel. + 358 10 6052 561
Soili Martikainen, Senior Safety Engineer, tel. +358 10 6052 419