Burlen 6v dry cell

I don't think you can do anything with them. But I may be wrong....

I've never had a problem with sealed batteries (other than them suddenly dying on me).

My Burlen batteries are years old and still working well - unlike other reputable sealed batteries which seldom seem to exceed 18 months.

First question is "does the bike have an electronic regulator"?

The original lighting system used a complicated light switch which switched alternator coils in an attempt to match output to load.

Headlamp = 3 pairs of coils in parallel.

Sidelight = one pair of coils only

No Lights = one pair of coils only but with the other two pairs shorted out to reduce the output.

At the end of the day it was crude. If more power was produced than was drawn then the only place the surplus power could go was in electrolysing the battery acid - spitting it into hydrogen and oxygen - heating the battery in the process. This is why you were supposed to top up your battery with distilled water at intervals. When 12V was introduced there was a lot too much power at least some of the time and the Zener diode was introduced. Basically some surplus power is dissipated in the form of heat but it is a rather basic device and some overcharging is likely to occur. A sealed battery won't take that punishment. It will last very well provided it is never overcharged so should not be fitted to any bike without an electronic regulator to prevent overcharging.

Hi Robert, yes, I've got a sealed 6V Burlen battery AND an electronic regulator. It's a totally reliable set up, never had a problem and the battery seems to keep its charge remarkably well. It's been on the bike since its rebuild eight or nine years ago, the solid state regulator added for seven of those years- the old Lucas one went bonkers and melted itself, like they all do eventually. Would certainly recommend, but wouldn't try surgery on it.