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I'm making a project/rc boat to map the bottom of a lake and therefore I need a relatively big battery (say 12V 10Ah) for the operation and electronics of the small boat (propeller motor + telecoms + servo rudder control + GPS + depth sensor + micro-controllers etc).

To make the boat more stable I would like to make the heavy batteries submerged in a sealed container along with the depth sensor.

From all the batteries I've searched LiFePO4 seems like the most viable choice.

Is this a wise choice for this particular application?

I recall everyone that the sealed container can be made in metal (no problems with weight/mass) hence it would always act as a heat dissipation for the batteries therefore reducing possible damage due to high temps.

Is there something that I'm missing about this type of batteries that would not make then suitable for such an application? The boat/rover would have on top a solar panel to recharge at least a bit the boat making it way more autonomous in the lake and hence avoiding annoying recharging of the battery on shore. So the battery would operate sealed and recharging while submerged. Thanks in advance for your comments.

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Nothing wrong with LFP batteries. Their beauty is that they don't blow up or burst into flames when things go wrong. That said, what could go wrong...?

Why are you worried about temperature? If they are getting hot, you're doing it wrong.

Perhaps a wide-ish PVC pipe, the same inner diameter as the battery length (or batteries), going straight down. The one end is given a properly sealed end-cap with PVC weld. The other end can be on the surface, with a big, plumbing screw-on cap.

Holes are drilled in the cap, wires pulled through, and you silicone around that wires to protect from splashes.

But going back to the battery, if weight isn't a terrible issue, a 12V 10AH SLA battery would be perfectly fine. It would likely have similar weight to an LFP.

Stick on a 20W panel and a solar controller, and you have power sorted. Even if it couldn't make the thing fully "unplugged", it would extend the running time well, wouldn't be difficult to implement, and would be roughly the same price as similar sized LFP batteries.

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  • \$\begingroup\$ Yup my thought exactly. I intend to buy a commercial grade charge controller with temperature control feedback. So that should not be a problem. Also I mentioned the metal pipe/container simply because that same metal would act as a radiator, very good thermal conductivity. The PVC pipe was also my first thought, the metal one is well a bit overkill. \$\endgroup\$ – Strider Jan 30 '18 at 14:09
  • \$\begingroup\$ About the SLA batteries, well there I truly do not think could be safe. My search in here (stackexchange and online) shows many references that the sealed led acid batteries can and will leak hydrogen. So that can be a hazard deep down (1m/2feet) under. Ventilation issues can make that a problem. If that was not my concern I would not use of course the much more expensive LiFePO4 batteries. \$\endgroup\$ – Strider Jan 30 '18 at 14:13
  • \$\begingroup\$ @Strider I sort of disagree. I used the cheapest 12V SLAs for their size, price, and convenient packaging in solar systems and tracked robots with issue. Though never pushing them to their limits, I did abuse them in many cases, using them beyond their recommended 3-year service life in a solar-power system (which is exactly what your average Chinese SLA SHOULDN'T be used for. And yet...) \$\endgroup\$ – Hoets Feb 1 '18 at 6:23
  • \$\begingroup\$ @Strider Are we talking about a submarine? I thought this is a surface craft with parts partially submerged for balance. SLAs fail when their charge controllers fail and keep charging them beyond their safe voltage - the result is that the extra energy can't go anywhere, you get heat, and the acid inside begins to boil. \$\endgroup\$ – Hoets Feb 1 '18 at 6:32
  • \$\begingroup\$ @Strider But that is just my opinion with regards SLAs. What about the idea of using metal? PVC offers many benefits, in that it is easy to seal, light, easy to buy in various shapes, and it won't corrode. Why are you worried about temperature? If something is overheating, something is very wrong, regardless of what battery is being used. \$\endgroup\$ – Hoets Feb 1 '18 at 6:36

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