Low quiescent 12VDC->5VDC step down module, plus weatherproof - product or DIY?

[mortrek]

I'm trying to make an outdoor rig which runs off of a lead acid battery but it takes a USB/5V input. The device has low, intermittent current usage, so the adapter does not need a high current capacity.

I wanted to find a 12VDC->5VDC step down module that was potted/weatherproof, but all I've found so far are cheapo ones with 10mA quiescent current. I want the rig to run for a year or more. Normally it runs off of AA lithiums, which have 2000mAh or so capacity, and they only work for about 3 months. Even a smallish marine battery would last much longer, unless of course the adapter has a high quiescent current, thus my problem.

Is there such a product available, or do I need to make my own from scratch or even get a good efficient one (from say Pololu) and pot it myself in potting compound/put it into a weatherproof housing? What would you recommend?

If my entire premise is flawed, please let me know. I'd be fine with a small recharageable lithium battery + solar charger, but all of the solutions I've found have been very lacking in reliability and/or weatherproofing.

Edit:

Example of non-weatherproof module I could consider: https://www.pololu.com/product/2850 - put it in a small ip65+ case with small drilled holes, put wires through, seal with silicone, or pot it and hope it doesn't overheat...

[pigrew]

Some CUI modules are a bit better, for example the VX7805-500 (which is already potted), and has about 0.3 mA quiescent current. However, maybe an ultra-low IQ LDO would be better, even with the inefficiency of the linear regulation.

Also do think about the self-discharge rate of lead acid batteries. Lithium primary cells have much lower self-discharge and would have a voltage closer to your target.

There are suitable converters from Linear Technologies and TI, but they're less likely to be available in easy-to-solder pre-built modules. For example, the
LMZ21700 has ~30 uA Iq, but you'd have to weatherproof everything yourself.

[jhpadjustable]

The weatherproofing is the better-known aspect so I'll treat it as solved. Almost all switching converter ICs offer an enable/shutdown input, though few modules expose it to the user. On most modules, you can lift the pin and connect your own controls to it.

What event or condition starts the high-current period?

Do you have a signal that you can see ahead of the high-current period, or can you delay the high-current activities for a brief moment? A few milliseconds would be enough.

Is it feasible to turn the entire load on and off in response to that signal? Alternatively, is it feasible to run an LDO all the time and enable the switching converter only during the high-current periods, using a Schottky diode on each one's output to avoid back-powering the other and any possibility of grief due to that?