Why do head torches have THREE batteries?

[horizon]

The problem is as JohnW pointed out above is that three batteries leaves you with either one spare or one short in a normal two-four world (the mini battery charger I take with me takes just two). Certainly buying three four-packs would get you four sets of three batteries but I use rechargeables.

But thank you meic for explaining!

[mercalia]

because its the first odd prime number - question answered?

[meic]

Mine takes one battery, here are a couple that take four batteries.
http://www.ebay.co.uk/itm/Genuine-LED-L ... Swo0JWN5BY
https://rockrun.com/products/black-diam ... -headtorch

[JohnW]

Although despite the very interesting replies, I still don't know why.

Ah - well - you didn't ask why it was, you asked if it was annoying - or to be correct, whether we agreed that it's annoying.................nobody answered that

meic has suggested a reason why the manufacturers do it..........but is there a consensus on whether it's annoying?

[thirdcrank]

The explanation is so simple that there may have been some knowledge taken for granted.

A cell can only have a single nominal voltage. Afaik, your standard dry cell Duracell or whatever is 1.5 volts, (but that gradually drops with use or more slowly with storage.) Other types vary a bit so NiCads = 1.2 volts. I don't know about any others.

A "light source" requires a certain voltage to work. Traditional bulbs (with a filament) can be made to require different voltages and they are forgiving, in that as the power fades so do they. Conveniently, bulbs can be matched with cells in multiples of two (or other numbers) AFAIK, LED's have more stringent requirements in that the power can only flow one way and it needs to be more precisely matched to their requirements.

Back to rjb's illuminating and lucid reply: it typically takes three cells to provide the voltage to power an LED lamp.

[simonineaston]

Annoying, isn't it?

With respect, folks, Horizon isn't asking for an explanation - he's asking for sympathy. And I for one agree, although I took steps to ammeleriote the annoyance, by investing in 12 Eneloop batteries... I have to admit though, that Horizon could have steered our empathy better but asking not two, but one single question.

[RickH]

Since moving on to buying Eneloops or Panasonic version of them six years ago, I have not had any of those batteries fail to deliver. They will, I imagine, still get ruined if left in a multi-battery device to depletion.

I'll echo that. Since buying low self discharge NiMH rechargeables in 2008 (in my case mostly Ansmann Max-e) I can't recall a single failure. I use them in virtually everything I can - even TV remote & clocks as they don't, as the name suggests, self discharge. Plus they are supposed to be better at holding charge in cold conditions which is good for bike lights in winter.

Intelligent chargers that charge each cell separately helps longevity too and means you CAN charge 3 at a time!

[horizon]

Annoying, isn't it?

With respect, folks, Horizon isn't asking for an explanation - he's asking for sympathy. And I for one agree, although I took steps to ammeleriote the annoyance, by investing in 12 Eneloop batteries... I have to admit though, that Horizon could have steered our empathy better but asking not two, but one single question.

OK, OK ... so this is how it should be:

Head torches have three batteries. Annoying isn't it? So why do they?

[freiston]

My head torch takes 1 AA. My decision when buying it was whether to go for 'regular' batteries (like AA or AAA) or more powerful alternatives such as CR123, 14500. I went for the single AA because AAA lights are a PITA due to low capacity and the tendency to take three batteries and also because I often have something else that takes AA batteries. I didn't go for the rarer battery types because a) they are rarer and b) I don't need the power - I don't use a head torch primarily as illumination to see the way on the bike but more to see things when I'm using my hands for other things (and if I'm using my hands, then it is usually close-up use). Saying that, my head torch is powerful enough to see the way by and powerful enough for use as a general purpose torch.

I wanted something small/compact, easily pocketable, fuss-free, tough and waterproof. I ended up getting a IPX-8 waterproof-rated metal-bodied Fenix HL23 and the specs are (quoted from torchdirect.co.uk):

Using 1 x AA NiMH rechargeable battery:
High: 150 lumens; 1 hour, 20 minutes run-time
Mid: 50 lumens; 5 hours, 40 minutes run-time
Low: 3 lumens; 100 hours run-time

Using 1 x AA alkaline battery:
High: 150 lumens; 1 hour run-time
Mid: 50 lumens; 4 hours, 25 minutes run-time
Low: 3 lumens; 110 hours run-time

I'm really happy with it and would recommend it - but it isn't a floodlight, just a decent torch that you can wear on your head.