Any new lighter 12v battery options?

The voltage regulator is a good idea.  Is this the one you're referring to?

https://www.fpv-power.com.au/kayakbatteries/index.php?route=product/product&path=24_60&product_id=58

Rory, check out this video.  Tim is the guy who peaked my interests in the FPV power batteries.  They are completely waterproof and the mounting system on a Hobie is just sweet.  About 4 mins and 35 seconds in he talks about the voltage regulator that was best for his system.

I actually just received this battery.  Interested to try it out.  Good bit larger than the 9800mah version.  Do you use a "smart" charger or the one that came with the battery? 

I use the one that came with it. I am a bit cautious about the whole thing and only charge it when I am home and can monitor it if necessary. With that being said I have looked into buying a smarter charger for it, however I haven't found one yet that fits the bill. Neverthless it's a Li-Ion battery rather than a LIPO of LIFEPO4 battery so assuming you keep it safe from water and puncture it should be rock solid.

I actually just received this battery.  Interested to try it out.  Good bit larger than the 9800mah version.  Do you use a "smart" charger or the one that came with the battery? 

I use the one that came with it. I am a bit cautious about the whole thing and only charge it when I am home and can monitor it if necessary. With that being said I have looked into buying a smarter charger for it, however I haven't found one yet that fits the bill. Neverthless it's a Li-Ion battery rather than a LIPO of LIFEPO4 battery so assuming you keep it safe from water and puncture it should be rock solid.

OK, the Li-ion vs LIPO thing is a source of confusion for me.  It's advertised as li-ion, but right on the battery it says "lithium polymer", which, IIRC, is a LIPO.  Anyone know which it is? 

Of course, I didn't know the difference, this link helped:

http://blog.ravpower.com/2017/06/lithium-ion-vs-lithium-polymer-batteries/

But it's probably important to know what we're holding in our hands.  I'm guessing go with the label, which would mean it's a LIPO.

As for charging, I have an older "smart" charger because I vaguely remember hearing there was no overcharge protection on the stock one.

https://www.ebay.com/itm/12-6V-5A-Li-ion-Battery-smart-charger-12V-5A-Charger-for-3S-18650-battery/
( that looks like it but I am not 100% sure it's the same one)

I found a 2016 thread where rawkfish was saying he used this one:

https://www.amazon.com/Professional-discharger-Aluminium-Multi-axis-Aircraft/dp/B00XC62FFC/

Which looked interesting, because it would be a single charger for everything.  I decided to spring for this one:

https://www.amazon.com/Tenergy-Balance-Charger-Discharger-Connectors/dp/B00466PKE0/

Because it comes with the AC cable and is a bit newer.

Everything I have read says lithium iron phosphate (LiFePO4) batteries are safest. The chance of thermal runaway (fire) with lithium ion batteries exists. Manufacturers try to keep that chance low, like less than 1 in 200,000. I'd like those odds on a lottery ticket...but not on something that could sink my kayak.  LiFePO4 is heavier per amp-hour than Li-ion, but it's still far lighter than sealed lead-acid (SLA).

Yup, I'm still using that charger, Rory. I really like it so far. I was warned about knock-offs of it so if anyone wants to buy one make sure it's the original Imax B6.

Still using my home-made 18650 array too. It was kinda pricey and a bit of a project but I really like it.

Yup, I'm still using that charger, Rory. I really like it so far. I was warned about knock-offs of it so if anyone wants to buy one make sure it's the original Imax B6.

I got that Tenergy one, which I think is comparable?  But I am gonna return it - it's way above my pay grade.  You're an engineer, I'm just some dweeb.  The instructions are like..."if you press the wrong button...YOU WILL DIE.  If you fart while charging a LiPO battery...YOU WILL DIE".  So now I'm freaked out. 

I mean... It gets pretty good reviews on Amazon... Probably ok?
The way you get in trouble with those things is if you try and charge too quickly or too many cells. People try and recharge their drone batteries too quickly and in pumping too much current through things get hot and melt.
I set mine to charge Li-ion, 4 series, 4 parallel at about a 2 amp max charge current I think. Keep it low and slow and you'll be good to go.
I also have a fuse and battery management systems between my charger and batteries so the system has a lot of protection built in.

Brace yourself for interrogation...

what voltage is the charger set at (lets assume you're charging a blue brick)?
what amp fuse do you use btw the charger and battery?
Also what are the "battery management systems" you mention?
Do you know how many cells your typical blue brick battery has?  It's not immediately clear in the description or on the battery itself.

https://www.ebay.com/itm/Pro-DC12V-9800mAh-Rechargeable-Portable-Li-ion-Battery-US-Plug-Battery-Pack-EG/222383802270

And how many would this "fat boy" blue brick have?

https://www.ebay.com/itm/Portable-DC-12V-20000mAh-Li-ion-Super-Rechargeable-Battery-Pack-w-US-Plug-/263640044975?hash=item3d622bd5af

I am on NCKA alot, here is my version of lithium.
Capacity is true, no exaggeration here. Check it out.

http://www.norcalkayakanglers.com/index.php?topic=87570.0

Brace yourself for interrogation...

what voltage is the charger set at (lets assume you're charging a blue brick)?
I use the auto detect voltage feature of the charger. So I plug it in and hit start and it detects that the voltage is roughly 14 or 15 volts, so it asks if there are 4 series cells. I confirm yes and it goes to work. Its been a while since I have programmed it so I'd have to go back and refresh myself on how to work it. But that's one of the reasons I love it - program it once and it's just a matter of a button or two to use it - simple.
However, it's permanently set on the Li-ion function. I'm suspicious that the blue brick batteries are actually comprised of Li-polymer flat packs. I think, not sure, but I think that the Li-polymer flat packs might need a different charge program. Again, I'm not sure. I'd do some internet searching about how use the IMAX B6. The great thing about it is there is tons of stuff on the web about it because it's so popular.

what amp fuse do you use btw the charger and battery?
Since I charge at a max rate of two amps, I use a two amp fuse.

Also what are the "battery management systems" you mention?
Icstation 12.8V 14.4V 15A 4S Lithium Battery Protection PCB BMS Board for 18650 18550 Li-ion Lipo Battery Pack https://www.amazon.com/dp/B01N6O5732/ref=cm_sw_r_cp_apa_i_3mFWCbTJPZP8K
Each 4-series pack has one. Since the ncr18650 cells I'm using are unprotected, this board handles the overcharge, over discharge, over current  protection for each cell.

Do you know how many cells your typical blue brick battery has?  It's not immediately clear in the description or on the battery itself.

https://www.ebay.com/itm/Pro-DC12V-9800mAh-Rechargeable-Portable-Li-ion-Battery-US-Plug-Battery-Pack-EG/222383802270

And how many would this "fat boy" blue brick have?

https://www.ebay.com/itm/Portable-DC-12V-20000mAh-Li-ion-Super-Rechargeable-Battery-Pack-w-US-Plug-/263640044975?hash=item3d622bd5af

Again, I'm suspicious that these batteries could be Li-polymer flat packs wrapped up and sold as Li-ion because most people don't care or know the difference and they have their own charger. I'd need to see someone take one apart for me to be convinced that they are Li-ion. Lots of Li based batteries are 3.7 volts per cell. But since these things are wrapped up and appear to have their own bms, it's hard to know what is really going on under that blue plastic.

Are you thinking of charging the blue brick as it is with something like the IMAX B6?

Brace yourself for interrogation...

what voltage is the charger set at (lets assume you're charging a blue brick)?
That depend on the cell configuration.
what amp fuse do you use btw the charger and battery?
15A fuse is plenty for what we use on kayak.
Also what are the "battery management systems" you mention?
It's a circuit to cut off voltage when circuit short, over-current draw, over-discharge.
Do you know how many cells your typical blue brick battery has?  It's not immediately clear in the description or on the battery itself.
I have opened up a few blue brick myself. Their spec is amazing, however it's way over their claim. That's why it's cheap.
https://www.ebay.com/itm/Pro-DC12V-9800mAh-Rechargeable-Portable-Li-ion-Battery-US-Plug-Battery-Pack-EG/222383802270

And how many would this "fat boy" blue brick have?
$37 for a 20Ah battery. No way. I bet you will see 6 knock off cells.
https://www.ebay.com/itm/Portable-DC-12V-20000mAh-Li-ion-Super-Rechargeable-Battery-Pack-w-US-Plug-/263640044975?hash=item3d622bd5af

Are you thinking of charging the blue brick as it is with something like the IMAX B6?

Heh, the phrasing of your question confirms that I should not do this.  But yes, that was my original intention.

I tinkered with it, and it seems to auto-sense 3 3.7 cells.

I've been using the blue brick for a while with varying degrees of success.  The cheap chinese aspect of them still skeeves me out.  But when I tried an anker 12v power block it apparently destroyed my transducer.  At least the blue brick didn't do that.

Anyway, I got the charger because I thought it would be a one-charger-for-all: SLA, blue brick, lifepo4 (if I got one).  But, I think I'm over my head and I don't want to burn my house down.  My wife would be PISSED.

Are you thinking of charging the blue brick as it is with something like the IMAX B6?

Heh, the phrasing of your question confirms that I should not do this.  But yes, that was my original intention.

I tinkered with it, and it seems to auto-sense 3 3.7 cells.

I've been using the blue brick for a while with varying degrees of success.  The cheap chinese aspect of them still skeeves me out.  But when I tried an anker 12v power block it apparently destroyed my transducer.  At least the blue brick didn't do that.

Anyway, I got the charger because I thought it would be a one-charger-for-all: SLA, blue brick, lifepo4 (if I got one).  But, I think I'm over my head and I don't want to burn my house down.  My wife would be PISSED.

It isn't that you shouldn't do it, it's just that it's a much more complex charger than what you need to charge the blue bricks. Yeah, the auto sense of 3 cells makes sense, since it's probably detecting a voltage of around 11.1 volts (3*3.7). That charger will work just fine to charge your blue bricks. The bms of the blue brick SHOULD stop the charging once the pack reaches a certain internal voltage. Check out the charger that came with the blue brick. Look at the output power specs and just program your charger to provide that. It's probably something like 12v, 1 or 2 amps.
It's a great charger to have for what you want since it can charge them all.
Like Chet mentioned, the blue bricks on eBay and other sources are cheap and way over rated. Lithium batteries really are still pretty well priced at how many joules you'll get out of a pack. In most cases if it seems cheap, it's probably because it's over rated.

Knowing what I know here is what I would do if I were to buy battery.
I will buy a lead acid battery if I don't have enough money, or I only run small FF.
I will buy a legit lithium battery if I have to get a lithium battery with proper charger. Not all lithium charger are the same, I did test them out.

I will fucking stay away from blue-brick battery. This is where you hear lithium battery explodes. Stay away from knock off battery cells too.