HI Dave,

Thanks for that. I did buy a couple of 3s 2650mah 33C batteries from my local shop just before I left for a weeks holiday- where I am now- so can't wait to get back and give them a go.
I will check out your link as I would like bigger capacity batteries eventually.
I found the wattmeter I bought can also be used as a balancer which is a good double check- in fact after storage charging my batteries they were a bit out of balance.
Still lots to learn but all interesting.
Liked the Pilot Cutter by the way- heavy boat!
All the best...Ian

HI Ian
Glad to hear you are progressing with LiPo's. There is a good UK supplier of LiPo's that our club uses and I can confirm that they are full spec and good quality see:
http://www.aerobuddies.co.uk/index.php?cPath=40_53_99.
Hope this helps 😀

Thank you both for your helpful replies. I understand that LiPo's shouldn't be discharged below a certain point and I purchased an alarm similar to the Hobby King one from my local shop. I can also see that it might need to be mounted where it may be heard. Due to all the help I have received on this site (and from my local model shop owner) I do feel in a position to start using LiPo's, and I agree that after a certain amount of use it will probably become ingrained as to how long one can sail.
Dave, the esc's I shall be using are Mtronics 40amp Vipers, which I don't believe have a voltage cutoff- hence my question, but as I go on with this I shall go over to brushless and use esc's with a voltage cutoff and the info about them from you is reassuring.
I have everything I need now except the LIpo's, and they will have to wait as I have spent up my modelling budget until next month!

All the best...Ian

HI Ian
I totally agree with Peter. LiPos must never be over discharged as any resultant damage is cumulative.
Most brushless ESCs have a built in setting that allows you to set the cut off voltage for LiPos.
More recent brushed ESCs now also have a built in setting.

The cut off with an ESC reduces the power to the motor by restricting the throttle setting allowing you to return the craft to shore to replace the battery.
If you are buying new then I suggest you ask the question if you intend to use with LIPos.

The item suggested is typical of its type and feed back comments suggest its can be heard at some distance. in a model boat you may need to place it so that the beeps are not masked too much. You do need to listen for the beeps as there is no automatic shut off of the ESC so your battery will continue to discharge until you close the throttle. That said the system has been successfully used for some years and is reliable.

I would not recommend estimating the point at which a cell is discharged, there are far too many variables and with simple and relatively cheap equipment available, why would you want to risk damaging your batteries or model.

HI Ian, lipo batteries generally have a balance lead attached to them, for each cell, its Important to balance charge, as a reasonable charger will then ensure all cells are balanced equally. You can buy an alarm, such as buzzer, digital display or led etc if you are concerned about discharge. if you over discharge below (generally) 3.2v per cell the lipo will become useless. I have used lipos for some time, so have a "feel" for how long they will last, I have tried numerous devices, the most recent is this

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=18588

its very good, I generally use two lipo packs at a time, and recently got these alarms, I can now run the batteries safely to the max discharge, hope that helps!