".....it seemed to generalise without mentioning the the decisive parameters involved, including cost difference!..."
Um. Tricky to cover everything, in a 4 sentence comment!
There seems to be a grave shortage of balanced advice in all aspects of modern life - though no shortage of advice per se at all! In a field where technological change is proceeding it is even harder to gather a useful view. Comparisons which were true one year are incorrect the next, and I suggest that it would be very useful to update any advice on the board which covers batteries
Luckily there is one reasonably independent place we can go for a balanced view - the market. Although it is not perfectly unbiased, we can deduce that if some battery
technologies are surviving in that marketplace there must be a demand for them, and hence that these technologies are likely to be the best available ones for some specific task. We only need to determine what that is.
As a quick example, if you look at a major UK battery
supplier to the model hobby - Component Shop - you will find available:
NiMH - both standard and low self-discharge
Lead Acid (sealed)
Alkaline (probably Manganese)
All of these will be the 'best choice' for some application. Our interest is probably mainly with the first four.
There are many battery
features to take into account. The energy capacity that the battery
contains is one common figure, usually measured in amp-hours, but most people do not realise that that is only correct for a particular delivery rate. To make a motor go fast you need a battery
with a high current delivery rate - able to put out a lot of amps over a short time. Dry batteries
, for instance, do not usually have a high delivery rate - hence the poor performance available to us in the 1960s!
My top-of-my-head generalisations are below, though I am sure exceptions can be found in all cases! 'Robust' refers to a mix of physical strength and resistance to misuse, such as over-charging or excessive drain. I will try to use the words 'capacity' for the amount of energy stored in a battery
, and 'delivery' for the maximum rate at which that energy can be released...
SLA Very robust. Cheapest for high amp-hour capacity at 6 and 12V. Can do high delivery as well, Very heavy. Use for displacement boats, where the ballast weight is a positive benefit. Can do heavy discharge as well, but many small SLAs are designed for emergency equipment use, and expect to support a light discharge over 10-20 hours.
NiMH Fairly robust. Quite cheap for medium amp-hour delivery, and reasonable capacity. Low self-discharge costs are dropping and that technology seems to be expanding in the market, though they tend to be low amp delivery types. Some types can compete with Lipos for high amp delivery in the 30-40A range. Fairly heavy. Make sure that you buy a high-delivery type if that's what you need for motors. Low self-discharge types are good for emergency flashlights and RC transmitter
LiPo - Less robust. Best current choice for high amp delivery with low weight. Only readily-available type offering current delivery in the 100+ Amps range. Light
, and available in very small sizes. More expensive than NiMH, high capacity very much more, and you need a special charger
, though these can be quite cheap nowadays. You should really be using a charger
optimised to your battery
type anyway. Remember that each LiPo cell is 3-4V, not 1.2V...
LiFE - Similar to LiPo, but more robust. Slightly lower voltage, but very flat volt delivery. Typical current delivery in the 30A range rather than 100+. More expensive than LiPo at the moment, but may displace them eventually.
LiPos are essential if you are using a very high consumption motor - perhaps a racing boat? But when using such currents you usually require cooling systems and quite a specialist drive train. Brushless motors can take high currents, so LiPos are often associated with them, but you can use any battery
with any motor if you want - just so long at it delivers the amps! There is no reason why you should not use brushless with SLAs, or LiPos on a low-drain application - though a LiPo may be more expensive than you need for that...
NiMH are perfectly capable of making a boat plane - IF you ensure that the max amp delivery is adequate. You can, for instance, buy NiMh batteries
designed for wireless phones
with max output 500mA or less - these will disappoint you if you try to use them for motor power!
A handy rule of thumb for estimating optimum battery
discharge is to look at the capacity in Amp-hours. A low-drain battery
is probably designed to put that out over 20 hours, so divide the Ah by 20 to get an estimate of optimum current draw. A high-drain battery
is usually designed to output over 1 hour - so divide the Ah by 1 to get optimum amps. That's only a generality, of course, and the battery
spec sheet is the definitive place to look...
"...more likely that HE had shares in a LiPo company to be able to afford them back then..."
When it comes to electrical equipment I do have connections. 😊
If you think LiPos were expensive in the 2000s, you should try buying NiCad pen cells in the 1960s. Probably the most unusual battery
I have used was a pack of saline/manganese oxide cells from ex-RAF life jackets
, where the battery
was open to the water underneath the boat and you could speed it up by scattering salt in front of it....