Where can I find a modern regulator for my 82 Suzuki gs750? I might end up with the same problem.
I replaced mine with a Series type RR from a Polaris RZR and used a pigtail harness from a Bonneville to connect it. A Series type is a step up from a MOSFET regulator. Here's a little write up I've done to try and explain the differences:
Battery capacity is really only a part of the consideration. When the bike is running, it will be running on the stators ability to keep up with demand, and the reg/rec's ability to regulate the stators output efficiently and reliably. When choosing a Lithium battery, I would recommend choosing one close to the same CCA and A/h rating as the lead acid one supplied as OEM. Shorai specs can be found by searching: Battery Specifications - Shorai Lithium Batteries
And BTW, the original poster of this thread was handicapped from the get go, because the R/R he had was installed out of the air flow that is need to dissipate the heat..
The first thing you need to be sure of, is that the charging system is up to the task. Lithium batteries do not typically like poor charging systems (do not like, as in.....up in smoke). So you need to be sure your stator is putting out good, even AC volts across all three legs and is not grounded.
Second is your rectifier. Most OEM and aftermarket replacement RR's are shunt type. These have worked fine for years, but they tend to create heat, and heat raises resistance which creates more heat, and eventually results in failed components. Mosfet type rectifiers, like the ones that Yamaha put on the newer R1's are better because they more accurately control the excess current, but they still regulate the charging voltage by shunting, or dumping, the excess current to ground. A Series type regulator rectifiers actually interrupts the circuit.
To illustrate the difference I give you this very simplistic illustration. Lets say your battery is a 5 gallon bucket that has a 1 inch hole in the bottom of it. You have a garden hose which represents the stator and rectifier portion of the reg/rec. As you fill the bucket (battery) up with water, some of the water drains out of the hole in the bottom. This is the electrical demand (lights, ignition, fans.....heated grips will cause a bigger hole). At low rpm...or with the spigot slightly open..., the water going in the bucket may just be able to keep up with the demand, but if you open the spigot more (or increase rpm) the bucket fills up faster than it is draining out. Once the bucket is full, the excess water flow has to be dealt with. This is how the RR types would deal with it:
1. A shunt type - Once the bucket is full, it dumps the water (current) onto the ground by overflowing
2. MOSFET type - When the bucket is full, you direct the hose to pour onto the ground. More precise and accurate, but still, current is going to ground and making mud (heat in the reg/rec). As the bucket drains, you direct the flow back to the bucket.
3. A series type - This hose has a sprayer attached to the end. When the bucket gets full, you release the trigger and the flow stops. When the bucket drains down a bit, you turn the hose back on.
*this is a VERY crude depiction and is only to help visualize the process
The SH775 reg/rec from a Polaris Razor is a series type....but there are many aftermarket ones that claim to be a SH775 "replacement" but are actually shunt types in an SH775 housing. So if you buy one, buy a genuine Polaris part #4012941. It is a 35 amp rated RR and regulates at 14-15 VDC. You can buy a harness for a Triumph Bonneville, cut one end off and splice the harness into your stator wires and the positive and neg leads to your rectifier. The Triumph part# is T2500676. Below are pics of my application and a photo of the invoice for the parts from Bike Bandit. This set up should work as long as you have a 3 wire stator, and a 5 wire reg/rec. (In other words, I don't know how to make an old Honda with field wires on the stator, or reg/recs that have signal wires work with this set up)