3.7V VARO Powerplus Compatible Battery 2900mAh Li-ion

My Powerplus trimmer cuts out after a few seconds then comes back on — is the battery dying or is something else wrong?

That stop-start pattern on a 3.7V Li-ion cell is almost always thermal cutoff triggering under load, not a dead battery. The cell is small and the protection circuit trips fast when current draw spikes — especially if the trimmer line is too long or the head is partially jammed. Before replacing anything, trim the line back to the correct length and clear any debris from the cutting head, then try again. If it still cuts out, charge the battery fully and check that the pack is reaching 4.2V at the terminals before assuming the cell is the problem.

New replacement battery charges fine but the trimmer feels weaker than it used to — what's wrong?

A freshly installed Li-ion cell often needs two or three full charge and discharge cycles before it delivers full capacity. If the tool feels sluggish immediately after fitting a new cell, that's the most likely cause — not a faulty battery. It's also worth checking the contact pins on the tool side for corrosion or debris, since a poor connection causes voltage drop under load and mimics a weak battery. Run the battery down fully, charge it completely, and repeat that cycle twice before drawing any conclusions.

Charger light stays solid and won't switch off — is the battery actually fully charged or is it stuck?

On small single-cell Li-ion packs like this 3.7V unit, a charger that won't switch off usually means the cell voltage never reached the 4.2V cutoff threshold — either because the cell is deeply discharged or there's a poor contact between the pack and the charger. Pull the battery out, clean the contact points on both the pack and charger with a dry cloth, reseat it firmly, and watch whether the indicator changes behaviour within the first two minutes. If the charger immediately shows the same solid light with no transition at all, measure the cell voltage directly — a reading below 2.5V means the cell has over-discharged and may not recover.