Battery warning light

[Hondaman]

Good evening folks, ive noticed that my Battery lamp has started to flash occasionally. It seems to happen when either I'm coasting to a stop, or at a standstill in traffic. I've had the car since last October, and I think the Battery is fairly new. Any thoughts on what could be causing this? The car drives perfectly.

[Herbie]

Check tightness and cleanliness of Battery connections, the 'other ends' of the connections, the alternator connections and also the engine earth strap.

In fact, even if you don't see any signs of corrosion it's still a good idea to take each connection off in turn and use some emery paper to clean up the washers, nuts and bolts before reconnecting things again. There are some heavy currents flowing in these cables and just a small amount of dirt and/or corrosion can cause problems.

Once all connections are clean and tight, check 'standing' Battery voltage against the chart below and also check charging voltage when the engine is running (should be about 14.2 to 14.7).

If the voltages are out or the cleaning/tightening of connections didn't help, it could indicate a fault with the voltage regulator or diode pack in the alternator.

EDIT: Doh!! Three hours after posting this I've realised that I forgot to include the Battery voltage chart earlier, so here it is:

[iSalajee]

Hi,

as I write this, I have just finished changing the alternator on my 07 IS250. I had the Battery light on as well for a week. 

Listen for a whining sound by the alternator which would indicate the pulley bearing has gone 

or connect a multi-meter to the Battery and turn on every electrical item that you can. IF the voltage drops significantly, then your alternator will need replacing.  

I just changed the alternator and it was a very long process. Would defiantly recommend a garage as it’s quite tough to get to and remove. 

[chr15gb]

Must be the season of power problems. I'm just having a power problem in my IS250.

I have a wireless charger like this
https://www.amazon.co.uk/audbos-Automatic-Clamping-Accessories-Qi-Enabled/dp/B07HGR5HXX/ref=sr_1_22?keywords=wireless+car+charger&qid=1561497160&s=gateway&sr=8-22

I noticed the arms opening and closing (and charging pulsing on and off).

I turned everything electical off I could, Air Con, seats, lights etc and the regular pulsing of the wireless charger stopped and charged as normal.
As sooon as I turned evertthing else back on it started playing up again.

This is all with the engine running, no Battery lights on the dash at all.

I'm trying not to think of alternator, my Battery is on my Ctek MXS5.0 charger on a regeneration cycle overnight. fingers crossed.