The bike starts first time when I get home, typical. Maybe I flooded the plugs.

So, battery voltage with engine off: 12.89V
@ 5k: 14.8V
@ 5k full beam: 14.3V
@ idle full beam: 12.5V, sharp decrease to <12
@ engine off, full beam: 11.9V, continuous decrease until I stopped the test so no way of testing for 30 mins!

So guys if you are right it looks like I need a new battery?

And I checked out my rear bulbs, when I go from low to high beam the bulbs actually get dimmer. The font on them says: STANLEY 12V18/5W SHN JAPAN. But missed out some crucial info...on low beam only my right headlight comes on. So an issue with low beam relay?

Does anyone know if this this battery will do, or do I have to carry out checks on what my current battery is?

http://www.ebay.co.uk/itm/like/27142587 ... 0&ff14=108

Thanks

I would start with the headlight bulb. Rear lamps may dim slightly as the other electrical loads are added ie headlight highbeam, particularly when you appear to have only one lowbeam bulb, engine is idling (little charging) and probably a dud battery (no reserve capacity).

http://www.ebay.co.uk/itm/NEW-YUASA-OEM ... 1e737e510a

^^^ get one of those, slightly larger capacity battery than the YTX-7-BS (it's just 1cm taller IIRC, fits fine)

Ok got a new battery. Idle gives about 14.3V, switching to full beam does a similar thing, drops sharply to about 12.5, then continues to drop to about 12.2V. However with this battery, it stops here. I left it for 5 minutes, it varied between 12.18-12.28V.

An improvement, but is this still too low?

Not to mention, the black battery lead on my bike isn't long enough so can't actually fit the battery properly....don't know the proper name for this lead, but can I buy a longer lead from somewhere?

Did you fully charge the new battery before fitting? Your results indicate that the new battery is capable of supporting the bikes electrical load at engine idle, when the generating system's output is inherently low. Provided the battery voltage at 5000 rpm rises to more than 14 volts, I would suggest all is well.

Below are the best battery voltages you are likely to get at idle rpm, assuming a good fully charged battery:

No headlights - 14.0 volts
Low beam - 13.3 volts (13.0 volts with 2 x 55/60 watt bulbs)
High Beam - 12.7 volts

RPM to achieve 14.6 volts:

No headlights - 2000
Low Beam - 2500 (expect 3000 with 2 x 55/60 watt bulbs)
High beam - 3500

magg wrote:Did you fully charge the new battery before fitting? Your results indicate that the new battery is capable of supporting the bikes electrical load at engine idle, when the generating system's output is inherently low. Provided the battery voltage at 5000 rpm rises to more than 14 volts, I would suggest all is well.

Below are the best battery voltages you are likely to get at idle rpm, assuming a good fully charged battery:

No headlights - 14.0 volts
Low beam - 13.3 volts (13.0 volts with 2 x 55/60 watt bulbs)
High Beam - 12.7 volts

RPM to achieve 14.6 volts:

No headlights - 2000
Low Beam - 2500 (expect 3000 with 2 x 55/60 watt bulbs)
High beam - 3500

Yes of course I did :) there's a big difference between 12.2 and 12.7 volts though! The thing that still concerns me is, after the initial drop to about 12.8V, it continues to drop steadily for about 15 seconds (approx) til it hits 12.2V. Why does it drop like this over time?

The charge/discharge characteristics of lead-acid battery are:

1. 13.8V full charge gassing voltage, this is why the charging system should maintain at least 14 volts for the majority of the running time.

2. 12 volts is typical voltage at the end point of useful discharge period and varies with load, half hour or more with headlights on high beam and engine off.

3. 10.7 volts is a flat battery and should be avoided otherwise the battery may be damaged.

A stable battery voltage of 12.2 volts at idle with the headlight on high beam is ok. If you were to continue such a scenario eventually the battery will fall rapidly below 12 volts and the battery will be flat, but for all practical situations the charging system should recharge the battery whenever engine rpm rises above idle.

magg wrote:The charge/discharge characteristics of lead-acid battery are:

1. 13.8V full charge gassing voltage, this is why the charging system should maintain at least 14 volts for the majority of the running time.

2. 12 volts is typical voltage at the end point of useful discharge period and varies with load, half hour or more with headlights on high beam and engine off.

3. 10.7 volts is a flat battery and should be avoided otherwise the battery may be damaged.

A stable battery voltage of 12.2 volts at idle with the headlight on high beam is ok. If you were to continue such a scenario eventually the battery will fall rapidly below 12 volts and the battery will be flat, but for all practical situations the charging system should recharge the battery whenever engine rpm rises above idle.

Ok, I suppose I am never going to be on high beam at idle for 5 minutes anyway, let alone 2 minutes.

Thanks for your help with this guys. Now got to try and work out why low beam is pants, gonna look at the headlights this weekend.

You should get much better than 5 minutes out of the battery. The OEM 12V 6AH battery can in simple terms supply 6 amps for 1 hour. The load current for the NC30 headlight high beam should be around 10 amps, thus the battery voltage should not fall below 12 volts for at least 20 minutes. This is why the headlight high beam on with engine stopped is a good load test, as suggested earlier in this thread.